[DevTools] Migrate off of UI globals

The CL replaces uses of instances put on the global UI object in web
tests. Still uses `panels` which is non-trivial to replace, but accesses
the UI object on window instead of the global, so as to not clash with
the import.

Drive-by: Fix naming for a couple imports: XModule -> X

Bug: chromium:1442410
Change-Id: I7372a980a09fa95a8b11ea9163271496c75bb8d0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4905378
Reviewed-by: Simon Zünd <szuend@chromium.org>
Commit-Queue: Philip Pfaffe <pfaffe@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1205081}