Remove integer to pointer cast in Handle implementation

... so that Handle::from_raw is more friendly to miri tests with strict provenance.

Closes #996

Author: 06393993

ash/src/vk.rs

@@ -302,4 +302,9 @@ mod tests {
     fn test_debug_enum() {
         assert_eq!(format!("{:?}", vk::ChromaLocation::MIDPOINT), "MIDPOINT");
     }
+
+    #[test]
+    fn test_from_raw() {
+        let _ = <vk::Instance as vk::Handle>::from_raw(20);
+    }
 }

ash/src/vk/macros.rs

@@ -126,7 +126,7 @@ macro_rules! define_handle {
         #[repr(transparent)]
         #[derive(Eq, PartialEq, Ord, PartialOrd, Clone, Copy, Hash)]
         #[$doc_link]
-        pub struct $name(*mut u8);
+        pub struct $name(usize);
         impl Default for $name {
             fn default() -> Self {
                 Self::null()
@@ -137,20 +137,21 @@ macro_rules! define_handle {
             fn as_raw(self) -> u64 {
                 self.0 as u64
             }
+
             fn from_raw(x: u64) -> Self {
                 Self(x as _)
             }
         }
         unsafe impl Send for $name {}
         unsafe impl Sync for $name {}
         impl $name {
-            pub const fn null() -> Self {
-                Self(::core::ptr::null_mut())
+            pub fn null() -> Self {
+                Self(::core::ptr::null_mut::<u8>() as usize)
             }
         }
         impl fmt::Pointer for $name {
             fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-                fmt::Pointer::fmt(&self.0, f)
+                fmt::LowerHex::fmt(&self.0, f)
             }
         }
         impl fmt::Debug for $name {