Closes#7077.
This fixes the problem shown in #7077 where clearing a `TextEdit`
wouldn't reset its cursor position. I've fixed that by adding back the
`TextCursorState::range` method, which clamps the selection range to
that of the passed `Galley`, and calling it in the same places where it
was called before #5785.
(/cc @juancampa)
* [x] I have followed the instructions in the PR template
54fded362d