[linker] Improve *Invoker types linking (#3525)

Fixes: #3454

Context: #3525 (comment)

Improves fix of #3263

The fix in commit
4d8c28f
increased the apk size more than needed.  It marked all the
`*Invoker` types, because the `MarkJavaObjects` substep iterates over
all `Java.Lang.Object` derived types, before all the linking.

Turned out that the original regression came from the linker
itself. The new linker optimization was introduced in
dotnet/linker@13ea158
and so the `ITextWatcher` interface was not marked anymore.

> Interfaces on a type will no longer be marked simply because the
> type is marked. Instead, marking of interfaces on types is deferred
> until that interface type is marked for some other reason.

Before the new optimization, the linker preserved these
interfaces (like `ITextWatcher`) when marking the types based on them
(like `AbsListView` or `ITextWatcherImplementor` in this case).  That
also resulted in keeping the invoker interfaces in the assembly.  The
above mentioned optimization changed that.

Now they were linked out, because the interfaces implementation
are only accessed (during app runtime) after the invoker type is
loaded by `Type.GetType(string,bool)` in the native members
registration process.  The linker cannot know about that without XA
help during the linking.  The result of `ITextWatcher` being linked
away is that the `ITeextWatcherInvoker` type was linked away too.

It is now fixed by overriding the
`MarkStep.ShouldMarkInterfaceImplementation()` method, which returns
true for registered interfaces.  These interfaces are special for XA
in a way, that it can be, in some cases, reached only from Java side
and thus linker is unable to track the interface usage.  It is
similar to how linker handles the COM interfaces.

The crash in Topeka sample:

	System.TypeLoadException: Could not load type 'Android.Text.ITextWatcherInvoker' from assembly 'Mono.Android, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null'.
	  at (wrapper managed-to-native) System.RuntimeTypeHandle.internal_from_name(string,System.Threading.StackCrawlMark&,System.Reflection.Assembly,bool,bool,bool)
	  at System.RuntimeTypeHandle.GetTypeByName (System.String typeName, System.Boolean throwOnError, System.Boolean ignoreCase, System.Boolean reflectionOnly, System.Threading.StackCrawlMark& stackMark, System.Boolean loadTypeFromPartialName)
	  at System.RuntimeType.GetType (System.String typeName, System.Boolean throwOnError, System.Boolean ignoreCase, System.Boolean reflectionOnly, System.Threading.StackCrawlMark& stackMark)
	  at System.Type.GetType (System.String typeName, System.Boolean throwOnError)
	  at Android.Runtime.AndroidTypeManager.RegisterNativeMembers (Java.Interop.JniType jniType, System.Type type, System.String methods)
	  at Android.Runtime.JNIEnv.RegisterJniNatives (System.IntPtr typeName_ptr, System.Int32 typeName_len, System.IntPtr jniClass, System.IntPtr methods_ptr, System.Int32 methods_len)
	  at (wrapper managed-to-native) Java.Interop.NativeMethods.java_interop_jnienv_call_static_object_method_a(intptr,intptr&,intptr,intptr,Java.Interop.JniArgumentValue*)
	  at Java.Interop.JniEnvironment+StaticMethods.CallStaticObjectMethod (Java.Interop.JniObjectReference type, Java.Interop.JniMethodInfo method, Java.Interop.JniArgumentValue* args)
	  at Android.Runtime.JNIEnv.CallStaticObjectMethod (System.IntPtr jclass, System.IntPtr jmethod, Android.Runtime.JValue* parms)
	  at Android.Runtime.JNIEnv.CallStaticObjectMethod (System.IntPtr jclass, System.IntPtr jmethod, Android.Runtime.JValue[] parms)
	  at Android.Runtime.JNIEnv.FindClass (System.String classname)
	  at Android.Runtime.JNIEnv.AllocObject (System.String jniClassName)
	  at Android.Runtime.JNIEnv.StartCreateInstance (System.String jniClassName, System.String jniCtorSignature, Android.Runtime.JValue* constructorParameters)
	  at Android.Runtime.JNIEnv.StartCreateInstance (System.String jniClassName, System.String jniCtorSignature, Android.Runtime.JValue[] constructorParameters)
	  at Android.Text.TextWatcherImplementor..ctor (System.Object inst, System.EventHandler`1[TEventArgs] changed_handler, System.EventHandler`1[TEventArgs] before_handler, System.EventHandler`1[TEventArgs] after_handler)
	  at Android.Widget.TextView.add_TextChanged (System.EventHandler`1[TEventArgs] value)
	  at Topeka.Fragments.SignInFragment.InitContentViews (Android.Views.View view)
	  at Topeka.Fragments.SignInFragment.OnViewCreated (Android.Views.View view, Android.OS.Bundle savedInstanceState)
	  at Android.App.Fragment.n_OnViewCreated_Landroid_view_View_Landroid_os_Bundle_ (System.IntPtr jnienv, System.IntPtr native__this, System.IntPtr native_view, System.IntPtr native_savedInstanceState)
	  at (wrapper dynamic-method) Android.Runtime.DynamicMethodNameCounter.9(intptr,intptr,intptr,intptr)

The comparison of apk sizes with original and this fix (Topeka sample,
which was also used as repro):

| Version        | Size in bytes |
|----------------|--------------:|
| Before @4d8c28 |      21434941 |
| After  @4d8c28 |      28242405 |
| This fix       |      21638678 |

So the previous fix increased the apk size by around 6.5Mbytes, this
fix adds less than 199kbytes instead.

Author: radekdoulik

src/Xamarin.Android.Build.Tasks/Linker/MonoDroid.Tuner/Extensions.cs

@@ -120,14 +120,14 @@ private static bool IsRegisterAttribute (CustomAttribute attribute)
 			return true;
 		}
 
-		public static bool TryGetRegisterAttribute (this MethodDefinition method, out CustomAttribute register)
+		static bool TryGetRegisterAttribute (ICustomAttributeProvider provider, out CustomAttribute register)
 		{
 			register = null;
 
-			if (!method.HasCustomAttributes)
+			if (!provider.HasCustomAttributes)
 				return false;
 
-			foreach (CustomAttribute attribute in method.CustomAttributes) {
+			foreach (CustomAttribute attribute in provider.CustomAttributes) {
 				if (!IsRegisterAttribute (attribute))
 					continue;
 
@@ -138,6 +138,25 @@ public static bool TryGetRegisterAttribute (this MethodDefinition method, out Cu
 			return false;
 		}
 
+		public static bool TryGetRegisterAdapter (this TypeDefinition td, out string adapter)
+		{
+		       CustomAttribute register;
+		       adapter = null;
+
+		       if (!TryGetRegisterAttribute (td, out register))
+			       return false;
+
+		       if (register.ConstructorArguments.Count != 3)
+			       return false;
+
+		       adapter = (string) register.ConstructorArguments [2].Value;
+
+		       if (string.IsNullOrEmpty (adapter))
+			       return false;
+
+		       return true;
+		}
+
 		public static bool TryGetRegisterMember (this MethodDefinition md, out string method)
 		{
 			return TryGetRegisterMember (md, out method, out _, out _);
@@ -150,7 +169,7 @@ public static bool TryGetRegisterMember (this MethodDefinition md, out string me
 			nativeMethod = null;
 			signature = null;
 
-			if (!md.TryGetRegisterAttribute (out register))
+			if (!TryGetRegisterAttribute (md, out register))
 				return false;
 
 			if (register.ConstructorArguments.Count != 3)

src/Xamarin.Android.Build.Tasks/Linker/MonoDroid.Tuner/MarkJavaObjects.cs

@@ -192,8 +192,6 @@ void PreserveInvoker (TypeDefinition type)
 			if (invoker == null)
 				return;
 
-			Annotations.Mark (invoker);
-
 			PreserveIntPtrConstructor (invoker);
 			PreserveInterfaceMethods (type, invoker);
 		}

src/Xamarin.Android.Build.Tasks/Linker/MonoDroid.Tuner/MonoDroidMarkStep.cs

@@ -436,6 +436,14 @@ protected override void DoAdditionalMethodProcessing (MethodDefinition method)
 			PreserveRegisteredMethod (method.DeclaringType, member);
 		}
 
+		protected override bool ShouldMarkInterfaceImplementation (TypeDefinition type, InterfaceImplementation iface, TypeDefinition resolvedInterfaceType)
+		{
+			if (base.ShouldMarkInterfaceImplementation (type, iface, resolvedInterfaceType))
+				return true;
+
+			return resolvedInterfaceType.TryGetRegisterAdapter (out _);
+		}
+
 		protected override void DoAdditionalTypeProcessing (TypeDefinition type)
 		{
 			// If we are preserving a Mono.Android interface,