Clear the surface to transparent black when creating a PlatformViewWr…

…apper (#52047)

Without this, an opaque black surface may briefly flash onscreen when the platform view is shown (see internal issue b/332379081)

This matches the behavior used before to the introduction of PlatformViewRenderTarget in 2046254

That commit moved the clearing of the surface into SurfaceTexturePlatformViewRenderTarget.  But that caused surface clearing to happen in scenarios where there was no PlatformViewWrapper, resulting in the issue seen in flutter/flutter#141068

Later the surface clearing was removed from SurfaceTexturePlatformViewRenderTarget, causing the flashing black screen.

shell/platform/android/io/flutter/plugin/platform/PlatformViewWrapper.java

@@ -61,6 +61,16 @@ public PlatformViewWrapper(
       @NonNull Context context, @NonNull PlatformViewRenderTarget renderTarget) {
     this(context);
     this.renderTarget = renderTarget;
+
+    Surface surface = renderTarget.getSurface();
+    if (surface != null) {
+      final Canvas canvas = surface.lockHardwareCanvas();
+      try {
+        canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);
+      } finally {
+        surface.unlockCanvasAndPost(canvas);
+      }
+    }
   }
 
   /**