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 `TextField`s hit box. The `TextField`s default behavior is maintained outside of the context of `SearchAnchor/SearchBar`.

Fixes https://github.com/flutter/flutter/issues/128332 and #134965