Undo keyboard shortcut not working properly with the code formatting shortcut

[eclare]

When using the new code (backticks) formatting shortcut (related: #33300), the undo keyboard shortcut (Ctrl+Z on Windows) doesn't work as intended: it changes the text back to `foo` but then the text changes back to being an applied code formatting shortcut.

[afercia]

Thanks for the ticket @eclare. Reproduced consistently on trunk using different browsers on different platforms: the Undo button works, the shortcut Cmd/Ctrl+z doesn't.
On 4.5.3 sometimes works... specifically it worked for me on a previous version of Chrome (49) on Windows.

[iseulde]

In 39077:

TinyMCE: wptextpattern: Fix undo shortcut for inline patterns

Fixes #37092.