Added TabBar.splashFactory, TabBarTheme.splashFactory,overlayColor

[HansMuller]

Adds a splashFactory property to TabBar and adds splashFactory and overlayColor properties to TabBarTheme.

This enables defeating ink splashes by specifying splashFactory: NoSplash.splashFactory. The overlay color can be now be overridden for the pressed state, as well as the hovered and focused states (as before). For example, to create a TabBar that does not draw ink splashes, and only draws the default focused state highlight:

TabBar(
  splashFactory: NoSplash.splashFactory,
  overlayColor: MaterialStateProperty.resolveWith<Color?>(
    (Set<MaterialState> states) {
      // Use the default focused overlay color
      return states.contains(MaterialState.focused) ? null : Colors.transparent;
    }
  ),
  ...
)

Fixes #86661

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[darrenaustin]

Nice. LGTM.

[darrenaustin]

Interesting. I wonder if this might make a good candidate for a static function on MaterialStateProperty that could be used with any type.

[darrenaustin]

Nice. Funny that we didn't have this test already.

[HansMuller]

This PR failed a couple of internal tests that had configured InkWell.overlayColor with a MaterialStateProperty<Color> whose resolution depended on MaterialState.pressed. Previously this distinction was ignored and now it isn't. This caused a few golden image tests for widgets in the pressed state to fail.

Will break out the InkWell changes into a separate PR.

[pstromberg98]

@HansMuller I'm not super familiar with the material design spec but the PR looks good to me!

I thought I'd mention that setting the highlightColor to transparent in the nearest Theme ancestor seems to work. I'm surprised I didn't try that or if I was building with an older version of Flutter, I'm not sure. That being said I still think it makes more sense to utilize the MaterialStateProperty.pressed so I am still behind this PR!