[Xamarin.Android.Build.Tasks] delay ToJniName calls in ManifestDocume…

…nt (#7653)

Reviewing `dotnet trace` output for a `dotnet new maui` app:

    dotnet trace collect --format speedscope -- .\bin\Release\dotnet\dotnet.exe build -bl --no-restore foo.csproj

8.6% of the time in `<GenerateJavaStubs/>` is spent in:

    93.81ms xamarin.android.build.tasks!Xamarin.Android.Tasks.ManifestDocument.Merge(...)

Drilling down further, a lot of time is spent in:

    26.91ms java.interop.tools.javacallablewrappers!Java.Interop.Tools.TypeNameMappings.JavaNativeTypeManager.ToJniName(...)
     4.03ms java.interop.tools.javacallablewrappers!Java.Interop.Tools.TypeNameMappings.JavaNativeTypeManager.ToCompatJniName(...)

It looks like we call this code for *every* Java.Lang.Object subclass:

    var name        = JavaNativeTypeManager.ToJniName (t, cache).Replace ('/', '.');
    var compatName  = JavaNativeTypeManager.ToCompatJniName (t, cache).Replace ('/', '.');
    if (((string) app.Attribute (attName)) == compatName) {
        app.SetAttributeValue (attName, name);
    }

It looks like this code was originally here to solve a problem with
`Android.App.Application` classes that are missing an `[Application]`
attribute:

xamarin/monodroid@2a668b7

To improve this:

1. First check if we are a `Android.App.Application`, apply the above
   fixup and `continue`.

2. Find out if we are other types of interesting subclasses, where a
   `generator` is needed. `continue` otherwise.

3. Lastly, compute `name` & `compatName`. We are no longer doing this
   work for every type.

After these changes, I instead get:

    72.84ms xamarin.android.build.tasks!Xamarin.Android.Tasks.ManifestDocument.Merge(...)

This saves about ~21ms on incremental builds of `dotnet new maui`
projects.

src/Xamarin.Android.Build.Tasks/Utilities/ManifestDocument.cs

@@ -336,17 +336,20 @@ public IList<string> Merge (TaskLoggingHelper log, TypeDefinitionCache cache, Li
 				if (PackageName == null)
 					PackageName = t.Namespace;
 
-				var name        = JavaNativeTypeManager.ToJniName (t, cache).Replace ('/', '.');
-				var compatName  = JavaNativeTypeManager.ToCompatJniName (t, cache).Replace ('/', '.');
-				if (((string) app.Attribute (attName)) == compatName) {
-					app.SetAttributeValue (attName, name);
+				if (t.IsSubclassOf ("Android.App.Application", cache)) {
+					(string name, string compatName) = GetNames (t, cache);
+					if (((string) app.Attribute (attName)) == compatName) {
+						app.SetAttributeValue (attName, name);
+					}
+					continue;
 				}
 
 				Func<TypeDefinition, string, int, XElement> generator = GetGenerator (t, cache);
 				if (generator == null)
 					continue;
 
 				try {
+					(string name, string compatName) = GetNames (t, cache);
 					// activity not present: create a launcher for it IFF it has attribute
 					if (!existingTypes.Contains (name) && !existingTypes.Contains (compatName)) {
 						XElement fromCode = generator (t, name, targetSdkVersionValue);
@@ -481,6 +484,11 @@ SequencePoint FindSource (IEnumerable<MethodDefinition> methods)
 			}
 		}
 
+		(string name, string compatName) GetNames(TypeDefinition type, TypeDefinitionCache cache) => (
+			JavaNativeTypeManager.ToJniName (type, cache).Replace ('/', '.'),
+			JavaNativeTypeManager.ToCompatJniName (type, cache).Replace ('/', '.')
+		);
+
 		// FIXME: our manifest merger is hacky.
 		// To support complete manifest merger, we will have to implement fairly complicated one, described at
 		// http://tools.android.com/tech-docs/new-build-system/user-guide/manifest-merger