[linker] preserve interfaces on *Implementor types

Fixes: #7097
Context: xamarin/monodroid@a619cbe

Usage of a `Google.Android.Material.TextField.TextInputEditText`:

    var filterBox = FindViewById<TextInputEditText>(Resource.Id.filterBox);
    filterBox.TextChanged += (s, e) => { };

Crashes at runtime with:

    android.runtime.JavaProxyThrowable: System.TypeLoadException: Could not load type '{0}' from assembly '{1}'., Android.Text.ITextWatcherInvoker, Mono.Android, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null
        at System.RuntimeTypeHandle.GetTypeByName(String , Boolean , Boolean , StackCrawlMark& , Boolean )
        at System.RuntimeType.GetType(String , Boolean , Boolean , StackCrawlMark& )
        at System.Type.GetType(String , Boolean )
        at Android.Runtime.AndroidTypeManager.RegisterNativeMembers(JniType , Type , ReadOnlySpan`1 )
    --- End of stack trace from previous location ---
        at Java.Interop.JniEnvironment.StaticMethods.CallStaticObjectMethod(JniObjectReference , JniMethodInfo , JniArgumentValue* )
        at Android.Runtime.JNIEnv.FindClass(String )
        at Android.Runtime.JNIEnv.AllocObject(String )
        at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue* )
        at Android.Runtime.JNIEnv.StartCreateInstance(String , String , JValue[] )
        at Android.Text.TextWatcherImplementor..ctor(Object , EventHandler`1 , EventHandler`1 , EventHandler`1 )
        at Android.Widget.TextView.add_TextChanged(EventHandler`1 )
        at AndroidApp1.MainActivity.OnCreate(Bundle savedInstanceState)
        at Android.App.Activity.n_OnCreate_Landroid_os_Bundle_(IntPtr , IntPtr , IntPtr )
        at Android.Runtime.JNINativeWrapper.Wrap_JniMarshal_PPL_V(_JniMarshal_PPL_V , IntPtr , IntPtr , IntPtr )
        at crc64a6e0c00971f6cd91.MainActivity.n_onCreate(Native Method)
        at crc64a6e0c00971f6cd91.MainActivity.onCreate(MainActivity.java:29)

The problem being that the linker completely removed the
`ITextWatcher` interface, and the
`Android.Text.TextWatcherImplementor` type no longer implemented that
interface.

Reviewing the `MarkJavaObjects` linker step, the `PreserveImplementor`
merely preserved any methods named `*Handler`? I added code to
preserve interfaces with a matching name, such as: `ITextWatcher` ->
`TextWatcherImplementor`.

I updated a test for this scenario.

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

@@ -42,9 +42,7 @@ void ProcessType (TypeDefinition type)
 				return;
 
 			PreserveJavaObjectImplementation (type);
-
-			if (IsImplementor (type))
-				PreserveImplementor (type);
+			PreserveImplementor (type);
 
 			// If a user overrode a method, we need to preserve it,
 			// because it won't be referenced anywhere, but it will
@@ -264,24 +262,20 @@ void PreserveConstructors (TypeDefinition type, TypeDefinition helper)
 				PreserveMethod (type, ctor);
 		}
 
-		static bool IsImplementor (TypeDefinition type)
-		{
-			return type.Name.EndsWith ("Implementor", StringComparison.Ordinal) && type.Inherits ("Java.Lang.Object");
-		}
-
 		static bool IsUserType (TypeDefinition type)
 		{
 			return !MonoAndroidHelper.IsFrameworkAssembly (type.Module.Assembly.Name.Name + ".dll");
 		}
 
 		void PreserveImplementor (TypeDefinition type)
 		{
-			if (!type.HasMethods)
+			if (!type.Name.EndsWith ("Implementor", StringComparison.Ordinal) || !type.Inherits ("Java.Lang.Object"))
 				return;
-
-			foreach (MethodDefinition method in type.Methods)
-				if (method.Name.EndsWith ("Handler", StringComparison.Ordinal))
-					PreserveMethod (type, method);
+			if (!type.HasInterfaces)
+				return;
+			foreach (var iface in type.Interfaces) {
+				Annotations.Mark (ifaceType.Resolve ());
+			}
 		}
 	}
 }

tests/MSBuildDeviceIntegration/Resources/LinkDescTest/MainActivityReplacement.cs

@@ -115,6 +115,9 @@ protected override void OnCreate(Bundle bundle)
 			// [Test] Post
 			Android.Util.Log.Info(TAG, HttpClientTest.Post ());
 
+			// [Test] TextChanged
+			Android.Util.Log.Info (TAG, MaterialTextChanged.TextChanged (this));
+
 			var cldt = new CustomLinkerDescriptionTests();
 			Android.Util.Log.Info(TAG, cldt.TryAccessNonXmlPreservedMethodOfLinkerModeFullClass());
 			Android.Util.Log.Info(TAG, LinkTestLib.Bug21578.MulticastOption_ShouldNotBeStripped());

tests/MSBuildDeviceIntegration/Resources/LinkDescTest/MaterialTextChanged.cs

@@ -0,0 +1,18 @@
+using System;
+using Android.Content;
+using Google.Android.Material.TextField;
+
+public class MaterialTextChanged
+{
+	// [Test]
+	public static string TextChanged (Context context)
+	{
+		try {
+			var view = new TextInputEditText (context);
+			view.TextChanged += (s, e) => { };
+			return $"[PASS] {nameof (MaterialTextChanged)}.{nameof (TextChanged)}";
+		} catch (Exception ex) {
+			return $"[FAIL] {nameof (MaterialTextChanged)}.{nameof (TextChanged)} FAILED: {ex}";
+		}
+	}
+}

tests/MSBuildDeviceIntegration/Tests/InstallAndRunTests.cs

@@ -421,6 +421,24 @@ public class LinkModeFullClass {
 					new BuildItem ("ProjectReference", "..\\Library1\\Library1.csproj"),
 					new BuildItem ("ProjectReference", "..\\LinkTestLib\\LinkTestLib.csproj"),
 				},
+				PackageReferences = {
+					KnownPackages.AndroidXMigration,
+					KnownPackages.AndroidXAppCompat,
+					KnownPackages.AndroidXAppCompatResources,
+					KnownPackages.AndroidXBrowser,
+					KnownPackages.AndroidXMediaRouter,
+					KnownPackages.AndroidXLegacySupportV4,
+					KnownPackages.AndroidXLifecycleLiveData,
+					KnownPackages.XamarinGoogleAndroidMaterial,
+				},
+				Sources = {
+					new BuildItem.Source ("MaterialTextChanged.cs") {
+						TextContent = () => {
+							using (var sr = new StreamReader (typeof (InstallAndRunTests).Assembly.GetManifestResourceStream ("Xamarin.Android.Build.Tests.Resources.LinkDescTest.MaterialTextChanged.cs")))
+								return sr.ReadToEnd ();
+						},
+					},
+				},
 				OtherBuildItems = {
 					new BuildItem ("LinkDescription", "linker.xml") {
 						TextContent = () => linkMode == AndroidLinkMode.SdkOnly ? "<linker/>" : @"