Update FadeInImage to use new Image APIs (#33370)

This updates FadeInImage to use the new Image.frameBuilder
API (added in #33369), to greatly simplify the implementation
of FadeInImage.

This also removes the FadeInImage.placeholderSemanticLabel property.
This property was added in #28799 for the sake of completeness (the bug
it fixed was the lack of any semantic label support in FadeInImage), but a
placeholder is a transient visual artifact, not something that affects the
underlying semantic meaning of the image.

packages/flutter/test/painting/image_test_utils.dart

@@ -49,3 +49,8 @@ Future<ui.Image> createTestImage() {
   ui.decodeImageFromList(Uint8List.fromList(kTransparentImage), uiImage.complete);
   return uiImage.future;
 }
+
+class FakeImageConfiguration implements ImageConfiguration {
+  @override
+  dynamic noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
+}