Cherry-pick "[SuperEditor][SuperReader][Android] Fix scroll physics (Resolves #1539) (#1541)" to stable

[angelosilvestre]

This PR cherry-picks "[SuperEditor][SuperReader][Android] Fix scroll physics (Resolves #1539) (#1541)" to stable.

[matthew-carroll]

@angelosilvestre we seem to have failing tests

[angelosilvestre]

@matthew-carroll We have two failing tests that seems to be related to the new flutter version:

The first seems to be that Colors.grey now returns a MaterialColor:

SuperEditor floating cursor shows grey caret when far from text
══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following TestFailure was thrown running a test:
Expected: MaterialColor:<MaterialColor(primary value: Color(0xff2196f3))>
  Actual: Color:<Color(0xff6750a4)>

The second is a temporary code I added when Flutter didn't report a specific selector:

           // TODO: remove this code after Flutter's next stable version.
          // In Flutter 3.13, released in August 2023, this selector isn't generated during tests yet.
          // Simulate a performSelector call from the IME.
          await TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger.handlePlatformMessage(
            SystemChannels.textInput.name,
            SystemChannels.textInput.codec.encodeMethodCall(
              const MethodCall('TextInputClient.performSelectors', <dynamic>[
                -1,
                ['deleteBackwardByDecomposingPreviousCharacter:']
              ]),
            ),
            (ByteData? data) {/* response from framework is discarded */},
          );

I can open another PR fixing those issues.

[matthew-carroll]

@angelosilvestre If you'd like to fix the issue in another PR, then please go ahead and raise that PR and merge it first, then we can merge this one with passing tests.

[matthew-carroll]

@angelosilvestre I re-ran these tests after merging in your other stable PR with fixes, but it looks like we still have failing tests. Not sure which ones.

[angelosilvestre]

@matthew-carroll A rebase was needed.

Done.