Even though both are allowed in the style guide, it recommends to use
'using', as its syntax is more consistent with the rest of C++.
This CL turns all typedefs in src/debug to 'using' declarations.

R=jgruber@chromium.org

Bug: v8:8834
Change-Id: I205e14a0b230a26119e5b209a2bcec493a8815e3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1545901Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60698}