Fix SegmentedButton default size and default tappable size

[QuncCccccc]

fix #121493

SegmentedButton uses TextButton for each segments. When we have MaterialTapTargetSize.padded for TextButton, we make sure the minimum tap target size is 48.0( this value can be adjusted by visual density), even tough the actual button size is smaller. When SegmentedButton paints segments by using MultiChildRenderObjectWidget, it also includes the tap target size so the button that it actually draws always has the same height as the height of the tap target size.

To fix it, this PR firstly calculate the actual height of a text button in SegmentedButton class, then we can get the height delta if there is. Then the the value of (Segmented button render box height - the delta) would be the actual button size that we should see.

For now, we are not able to customize the min, max, fixed size in SegmentedButton style. So the standard button height is always 40 and can only be customized by style.visualDensity and style.tapTargetSize; SegmentedButton only simulates the TextButton behavior when TextButton's height is its default value.

SegmentedButtonDemo.mov

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
• I signed the [CLA].
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is [test-exempt].
• All existing and new tests are passing.

[HansMuller]

LGTM

[HansMuller]

Could be initialized using the new switch expression:

    final double tapTargetVerticalPadding = switch (resolvedTargetSize) {
      MaterialTapTargetSize.shrinkWrap => 0,
      MaterialTapTargetSize.padded => max(0, kMinInteractiveDimension + densityAdjustment.dy - effectedButtonHeight);
    };

[HansMuller]

Might be better to not that the button's height is 40 but its tap target's height is 48. Like:
'Min button hit target height is 48 and min (painted) button height is 40'

[HansMuller]

If 43.5 and 4.5 correspond to something can identify here, then best to include that info in the comment.