Editor: When switching Editor tabs, don't scroll unnecessarily.

- When switching to the Text view, wait until after the Visual editor element has been hidden, before focussing the `<textarea>`.
- When switching to the Visual view, only scroll if the cursor is not visible on the current screen.

Fixes #42530.


Built from https://develop.svn.wordpress.org/trunk@42175


git-svn-id: https://core.svn.wordpress.org/trunk@42005 1a063a9b-81f0-0310-95a4-ce76da25c4cd