Make Shift+Tab focus previous element before token selector

This is a follow up to !2883 (merged).

A minor problem with the current solution is that Shift-Tab and Tab have the same behaviour, which is to focus the input.

I would expect that Shift-Tab would allow you to navigate backwards through the document, but it just goes back and forth between the input and last token:

Peek_2022-06-16_14-34