Reland https://github.com/flutter/flutter/pull/141818 with a fix for a special case: If only `background` is specified for `TextButton.styleFrom` or `OutlinedButton.styleFrom` it applies the button's disabled state, i.e. as if the same value had been specified for disabledBackgroundColor.

The change relative to #141818 is the indicated line below:
```dart
final MaterialStateProperty<Color?>? backgroundColorProp = switch ((backgroundColor, disabledBackgroundColor)) {
  (null, null) => null,
  (_, null) => MaterialStatePropertyAll<Color?>(backgroundColor), // ADDED THIS LINE
  (_, _) => _TextButtonDefaultColor(backgroundColor, disabledBackgroundColor),
};
  ```

This backwards incompatibility cropped up in an internal test, see internal Google issue b/323399158.