Android: Bump default target SDK version to 34

The Google Play Store now requires apps to target at least SDK level 34
to be compliant with the latest "limitations and requirements".  Set our
default just as high so that apps can be published "out of the box".

This does imply that all apps built with `xbuild`'s default target SDK
level are supposed to be aware of the latest behaviour changes that they
opt into when specifying `targetSdkVersion=34`:
https://developer.android.com/about/versions/14/behavior-changes-14

Author: MarijnS95

xbuild/src/config.rs

@@ -133,7 +133,7 @@ impl Config {
         if let Ok(code) = VersionCode::from_semver(&package_version) {
             manifest.version_code.get_or_insert_with(|| code.to_code(1));
         }
-        let target_sdk_version = 33;
+        let target_sdk_version = 34;
         let target_sdk_codename = 13;
         let min_sdk_version = 21;
         manifest