This changes fixes text selection gestures on the search field when using SearchAnchor.

Before this change text selection gestures did not work due to an IgnorePointer in the widget tree.

This change:

• Removes the IgnorePointer so the underlying TextField can receive pointer events.
• Introduces TextField.onTapAlwaysCalled and TextSelectionGestureDetector.onUserTapAlwaysCalled, so a user provided on tap callback can be called on consecutive taps. This is so that the user provided on tap callback for SearchAnchor/SearchBar that was previously only handled by InkWell will still work if a tap occurs in the TextFields hit box. The TextFields default behavior is maintained outside of the context of SearchAnchor/SearchBar.

Fixes #128332 and #134965

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.