Use more code comments to better document generated assembler code.
This CL also attaches a CodeComment to FrameScope.

Change-Id: I45afc3e4078dc161316b877fbbd1ae8bcd6e821d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2964392Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Victor Gomes <victorgomes@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75277}