Just like the 2017 editor, we show the number of results and which one
is currently highlighted.
This patch also brings the Tab behaviour closer to the 2017 editor.
Hitting Tab from the search input focuses the replace input, followed by
the replacement buttons, then the find buttons, then the content
editable. Shift+Tab largely does the reverse, except Shift+Tab from the
editor doesn't bring you to the search panel. Doing this would require a
lot of work for minor benefit, as we'd need to determine which panel to
focus to.
Add basic unit test
Bug: T371436
Change-Id: I968f91320ecb6ab9e9da0994052d33c76f85974b
