Add ResizeImage.policy (#121154)

* Add ResizeImage.policy

This adds a new `ResizeImage.policy` property that controls how `ResizeImage`
will interpret its `width` and `height` properties. The existing behavior is
preserved via `ResizeImagePolicy.exact` (default), but there is now the option
to use `ResizeImagePolicy.fit`, which satisfies the use case outlined in
flutter/flutter#118543.

The API doc assets were added in flutter/assets-for-api-docs#209

Fixes flutter/flutter#118543

* Docuemnt public member

* Remove protected annotation from overrides - was failing tests

* Fixed analysis of code in Dartdoc

* More dartdoc code analysis fixes

* One more fix

* Review comments

packages/flutter/test/image_data.dart

@@ -48,7 +48,7 @@ const List<int> kAnimatedGif = <int> [
 // Constructed by the following code:
 // ```dart
 //  Future<void> someTest(WidgetTester tester) async {
-//    Uint8List bytes;
+//    Uint8List? bytes;
 //    await tester.runAsync(() async {
 //      const int imageWidth = 100;
 //      const int imageHeight = 100;
@@ -60,9 +60,9 @@ const List<int> kAnimatedGif = <int> [
 //      ui.decodeImageFromPixels(
 //        pixels, imageWidth, imageHeight, ui.PixelFormat.rgba8888,
 //            (ui.Image image) async {
-//          final ByteData byteData = await image.toByteData(
+//          final ByteData? byteData = await image.toByteData(
 //              format: ui.ImageByteFormat.png);
-//          bytes = byteData.buffer.asUint8List();
+//          bytes = byteData!.buffer.asUint8List();
 //          completer.complete();
 //        },
 //      );
@@ -91,3 +91,35 @@ const List<int> kBlueRectPng = <int> [
   99, 72, 140, 33, 49, 134, 196, 24, 18, 99, 72, 204, 5, 234, 78, 2, 198, 180,
   170, 48, 200, 0, 0, 0, 0, 73, 69, 78, 68, 174, 66, 96, 130,
 ];
+
+/// A portrait-mode (50x100) PNG with blue pixels.
+const List<int> kBluePortraitPng = <int> [
+  137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82, 0, 0, 0, 50, 0,
+  0, 0, 100, 8, 6, 0, 0, 0, 196, 232, 99, 91, 0, 0, 0, 4, 115, 66, 73, 84, 8, 8,
+  8, 8, 124, 8, 100, 136, 0, 0, 0, 140, 73, 68, 65, 84, 120, 156, 237, 207, 1,
+  13, 192, 48, 12, 192, 176, 126, 252, 57, 247, 36, 46, 45, 186, 108, 4, 201,
+  51, 179, 59, 63, 112, 110, 7, 124, 197, 72, 141, 145, 26, 35, 53, 70, 106,
+  140, 212, 24, 169, 49, 82, 99, 164, 198, 72, 141, 145, 26, 35, 53, 70, 106,
+  140, 212, 24, 169, 49, 82, 99, 164, 198, 72, 141, 145, 26, 35, 53, 70, 106,
+  140, 212, 24, 169, 49, 82, 99, 164, 198, 72, 141, 145, 26, 35, 53, 70, 106,
+  140, 212, 24, 169, 49, 82, 99, 164, 198, 72, 141, 145, 26, 35, 53, 70, 106,
+  140, 212, 24, 169, 49, 82, 99, 164, 198, 72, 141, 145, 26, 35, 53, 70, 106,
+  140, 212, 24, 169, 49, 82, 99, 164, 198, 72, 205, 11, 105, 8, 2, 198, 99, 140,
+  153, 87, 0, 0, 0, 0, 73, 69, 78, 68, 174, 66, 96, 130,
+];
+
+/// A landscape-mode (100x50) PNG with blue pixels.
+const List<int> kBlueLandscapePng = <int> [
+  137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82, 0, 0, 0, 100, 0,
+  0, 0, 50, 8, 6, 0, 0, 0, 170, 53, 126, 190, 0, 0, 0, 4, 115, 66, 73, 84, 8, 8,
+  8, 8, 124, 8, 100, 136, 0, 0, 0, 143, 73, 68, 65, 84, 120, 156, 237, 209, 65,
+  13, 0, 32, 16, 192, 176, 3, 255, 158, 225, 141, 2, 246, 104, 21, 44, 217, 154,
+  57, 103, 200, 216, 191, 3, 120, 25, 18, 99, 72, 140, 33, 49, 134, 196, 24, 18,
+  99, 72, 140, 33, 49, 134, 196, 24, 18, 99, 72, 140, 33, 49, 134, 196, 24, 18,
+  99, 72, 140, 33, 49, 134, 196, 24, 18, 99, 72, 140, 33, 49, 134, 196, 24, 18,
+  99, 72, 140, 33, 49, 134, 196, 24, 18, 99, 72, 140, 33, 49, 134, 196, 24, 18,
+  99, 72, 140, 33, 49, 134, 196, 24, 18, 99, 72, 140, 33, 49, 134, 196, 24, 18,
+  99, 72, 140, 33, 49, 134, 196, 24, 18, 99, 72, 140, 33, 49, 134, 196, 24, 18,
+  99, 72, 140, 33, 49, 134, 196, 92, 164, 190, 2, 98, 53, 3, 99, 174, 0, 0, 0,
+  0, 73, 69, 78, 68, 174, 66, 96, 130,
+];