[TextSelectionControls] move the tap gesture callback into _TextSelectionHandlePainter, remove `_TransparentTapGestureRecognizer`. (#83639)

This reverts commit 35ad43f2.

This reverts commit c26ed03c.

* Migrate to ChannelBuffers.push

* Move TestDefaultBinaryMessenger to its own file

* Apply deprecations and fix usages

This reverts commit a46139a2.

A very minimal right-click menu for Mac desktop.

When attempting to select a space on mobile, Flutter will try to select the word before the space too, if one exists.

Enables custom text selection menus by allowing selectionControls to be passed to TextField et. al.

SkParagraph may calculate slightly different metrics for text layouts

Flutter's `moreOrLessEquals` has a few advantages over `closeTo` from
the `matcher` package:

   * It emits the epsilon value in the test result on failure.
   * It uses a named parameter for epsilon, which improves readability
     at the call site.
   * It has a reasonable default for epsilon in cases where something
     more specific isn't required.

Using it also has the nice property that it aids in its own discovery
when when people go looking for such functionality in new tests.

This change also includes a couple unrelated whitespace formatting cleanups.