Editor: Improve scrolling behavior and prevent autosave logic from causing...

Editor: Improve scrolling behavior and prevent autosave logic from causing dirty state when just switching between Visual and Text tabs.

Props pento.
See #41962, #42029.
Fixes #42530 for trunk.

Built from https://develop.svn.wordpress.org/trunk@42183


git-svn-id: https://core.svn.wordpress.org/trunk@42013 1a063a9b-81f0-0310-95a4-ce76da25c4cd