Support materialTapTargetSize in PopupMenuButton

[hannah-hyj]

fix #128697

PopupMenuButton can take customized child, in that case if widgt.style.tapTargetSize is set to padded, PopupMenuButton should support it.

if child is null, default child is an iconButton, which is already 48x48.

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[QuncCccccc]

LGTM! Thanks for the fix!

[QuncCccccc]

I think here we can default to the ThemeData.materialTapTargetSize value. Then here would be final MaterialTapTargetSize tapTargetSize = widget.style?.tapTargetSize ?? popupMenuTheme.tapTargetSize ?? Theme.of(context).materialTapTargetSize; We can also add this property to PopupMenuTheme so developers can control the button size easier:)

Suggested change

	final MaterialTapTargetSize tapTargetSize = widget.style?.tapTargetSize ?? MaterialTapTargetSize.shrinkWrap;
	final MaterialTapTargetSize tapTargetSize = widget.style?.tapTargetSize ?? Theme.of(context).materialTapTargetSize;

[hannah-hyj]

I tried this but

if it defaults to Theme.of(context).materialTapTargetSize, this PR will be a breaking change because some buttons' size will be increased to at least 48X48, looks like some flutter_cacoon tests are failing because of that.(some g3 tests too.)

since I can't apply a flutter_cacoon fix together with this PR. I'm thinking the only way to land this PR with it default to Theme.of(context).materialTapTargetSize is by 4 steps.

1. Merge this PR with default to MaterialTapTargetSize.shrinkWrap so it's not a breaking change.
2. Update flutter_cacoon tests and g3 tests to use MaterialTapTargetSize.padded in its PopupMenuButton
3. Update PopupMenuButton to default to Theme.of(context).materialTapTargetSize
4. Remove now redundant MaterialTapTargetSize.padded in flutter_cacoon tests and g3 tests

wdyt?

[QuncCccccc]

I see. Sounds good to me! If we want to add this property to PopupMenuTheme, we can also add a separate PR later. This PR LGTM!