[android] avoid OnLayout() for Label (dotnet#21291)

Context: dotnet#18505
Context: https://github.com/dotnet/maui/files/13251041/MauiCollectionView.zip
Context: dotnet#21229 (review)

In profiling scrolling of an app with a `<CollectionView/>` and 12
`<Label/>`s, we see time spent in:

    1.9% Microsoft.Maui!Microsoft.Maui.Platform.MauiTextView.OnLayout(bool,int,int,int,int)

This is a callback from Java to C#, which has a performance cost.
Reviewing the code, we would only need to make this callback *at all*
if `Label.FormattedText` is not `null`. The bulk of all `Label`'s can
avoid this call?

To do this:

* Write a new `PlatformAppCompatTextView.java` that override `onLayout()`

* It only calls `onLayoutFormatted()` if a `isFormatted` `boolean`
  field is `true`

* We can set `isFormatted` if a formatted string is such as:
  `isFormatted = !(text instanceof String)`

With this change in place, the above `MauiTextView.OnLayout()` call is
completely gone from `dotnet-trace` output. Scrolling the sample also
"feels" a bit snappier.

This should improve the performance of all non-formatted `Label`s on
Android.

This is the mininum amount of API changes possible -- which seems like
what we should go for if we ship this change in .NET 8 servicing.

src/Core/AndroidNative/maui/src/main/java/com/microsoft/maui/PlatformAppCompatTextView.java

@@ -0,0 +1,44 @@
+package com.microsoft.maui;
+
+import android.content.Context;
+
+import androidx.annotation.NonNull;
+import androidx.appcompat.widget.AppCompatTextView;
+
+public class PlatformAppCompatTextView extends AppCompatTextView {
+    public PlatformAppCompatTextView(@NonNull Context context) {
+        super(context);
+    }
+
+    private boolean isFormatted;
+
+    /**
+     * Sets isFormatted=true, used for FormattedString content
+     * @param text
+     * @param type
+     */
+    @Override
+    public void setText(CharSequence text, BufferType type) {
+        isFormatted = !(text instanceof String);
+        super.setText(text, type);
+    }
+
+    @Override
+    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
+        super.onLayout(changed, left, top, right, bottom);
+
+        if (isFormatted) {
+            onLayoutFormatted(changed, left, top, right, bottom);
+        }
+    }
+
+    /**
+     * To be overridden from C#
+     * @param changed
+     * @param left
+     * @param top
+     * @param right
+     * @param bottom
+     */
+    protected void onLayoutFormatted(boolean changed, int left, int top, int right, int bottom) { }
+}

src/Core/src/Platform/Android/MauiTextView.cs

@@ -4,18 +4,16 @@
 
 namespace Microsoft.Maui.Platform
 {
-	public class MauiTextView : AppCompatTextView
+	public class MauiTextView : PlatformAppCompatTextView
 	{
 		public MauiTextView(Context context) : base(context)
 		{
 		}
 
 		internal event EventHandler<LayoutChangedEventArgs>? LayoutChanged;
 
-		protected override void OnLayout(bool changed, int l, int t, int r, int b)
+		internal override void OnLayoutFormatted(bool changed, int l, int t, int r, int b)
 		{
-			base.OnLayout(changed, l, t, r, b);
-
 			LayoutChanged?.Invoke(this, new LayoutChangedEventArgs(l, t, r, b));
 		}
 	}

src/Core/src/PublicAPI/net-android/PublicAPI.Shipped.txt

@@ -2253,7 +2253,6 @@ override Microsoft.Maui.Platform.MauiSwipeView.DispatchTouchEvent(Android.Views.
 override Microsoft.Maui.Platform.MauiSwipeView.OnAttachedToWindow() -> void
 override Microsoft.Maui.Platform.MauiSwipeView.OnInterceptTouchEvent(Android.Views.MotionEvent? e) -> bool
 override Microsoft.Maui.Platform.MauiSwipeView.OnTouchEvent(Android.Views.MotionEvent? e) -> bool
-override Microsoft.Maui.Platform.MauiTextView.OnLayout(bool changed, int l, int t, int r, int b) -> void
 override Microsoft.Maui.Platform.MauiWebChromeClient.Dispose(bool disposing) -> void
 override Microsoft.Maui.Platform.MauiWebViewClient.Dispose(bool disposing) -> void
 override Microsoft.Maui.Platform.MauiWebViewClient.OnPageFinished(Android.Webkit.WebView? view, string? url) -> void

src/Core/src/PublicAPI/net-android/PublicAPI.Unshipped.txt

@@ -26,6 +26,8 @@ Microsoft.Maui.KeyboardAcceleratorModifiers.None = 0 -> Microsoft.Maui.KeyboardA
 Microsoft.Maui.KeyboardAcceleratorModifiers.Shift = 1 -> Microsoft.Maui.KeyboardAcceleratorModifiers
 Microsoft.Maui.KeyboardAcceleratorModifiers.Windows = 16 -> Microsoft.Maui.KeyboardAcceleratorModifiers
 Microsoft.Maui.Layouts.FlexBasis.Equals(Microsoft.Maui.Layouts.FlexBasis other) -> bool
+Microsoft.Maui.PlatformAppCompatTextView
+Microsoft.Maui.PlatformAppCompatTextView.PlatformAppCompatTextView(nint javaReference, Android.Runtime.JniHandleOwnership transfer) -> void
 Microsoft.Maui.Platform.IImageSourcePartSetter
 Microsoft.Maui.Platform.IImageSourcePartSetter.Handler.get -> Microsoft.Maui.IElementHandler?
 Microsoft.Maui.Platform.IImageSourcePartSetter.ImageSourcePart.get -> Microsoft.Maui.IImageSourcePart?
@@ -64,10 +66,14 @@ override Microsoft.Maui.Handlers.ShapeViewHandler.GetDesiredSize(double widthCon
 override Microsoft.Maui.Layouts.FlexBasis.Equals(object? obj) -> bool
 override Microsoft.Maui.Layouts.FlexBasis.GetHashCode() -> int
 override Microsoft.Maui.MauiAppCompatActivity.DispatchTouchEvent(Android.Views.MotionEvent? e) -> bool
+override Microsoft.Maui.PlatformAppCompatTextView.JniPeerMembers.get -> Java.Interop.JniPeerMembers!
+override Microsoft.Maui.PlatformAppCompatTextView.ThresholdClass.get -> nint
+override Microsoft.Maui.PlatformAppCompatTextView.ThresholdType.get -> System.Type!
 override Microsoft.Maui.Platform.ContentViewGroup.GetClipPath(int width, int height) -> Android.Graphics.Path?
 override Microsoft.Maui.Platform.MauiMaterialButton.IconGravity.get -> int
 override Microsoft.Maui.Platform.MauiMaterialButton.IconGravity.set -> void
 override Microsoft.Maui.Platform.MauiScrollView.OnMeasure(int widthMeasureSpec, int heightMeasureSpec) -> void
+*REMOVED*override Microsoft.Maui.Platform.MauiTextView.OnLayout(bool changed, int l, int t, int r, int b) -> void
 override Microsoft.Maui.Platform.MauiMaterialButton.OnMeasure(int widthMeasureSpec, int heightMeasureSpec) -> void
 override Microsoft.Maui.Platform.NavigationViewFragment.OnDestroy() -> void
 override Microsoft.Maui.PlatformContentViewGroup.JniPeerMembers.get -> Java.Interop.JniPeerMembers!

src/Core/src/Transforms/Metadata.xml

@@ -5,12 +5,14 @@
   <!-- Make all classes internal by default -->
   <attr path="//class[@visibility='public']" name="visibility">internal</attr>
   <!-- Public classes -->
+  <attr path="//class[@name='PlatformAppCompatTextView']" name="visibility">public</attr>
   <attr path="//class[@name='PlatformContentViewGroup']" name="visibility">public</attr>
   <attr path="//class[@name='PlatformWrapperView']" name="visibility">public</attr>
+  <attr path="//class[@name='MauiViewGroup']" name="visibility">public</attr>
+  <!-- Internal methods & constructors -->
+  <attr path="//class[@name='PlatformAppCompatTextView']/method" name="visibility">internal</attr>
+  <attr path="//class[@name='PlatformAppCompatTextView']/constructor" name="visibility">internal</attr>
 
-  <!-- We subclass this so it needs to be public -->
-  <attr path="//package[@name='com.microsoft.maui']/class[@name='MauiViewGroup']" name="visibility">public</attr>
-
   <remove-node path="//package[@name='com.bumptech.glide']" />
   <remove-node path="//package[@name='com.microsoft.maui.glide']" />
   <remove-node path="//package[@name='com.microsoft.maui.glide.font']" />