For a ProvidedDiffChange, the AllFiles method naively returns all files
with rglob("*"). The returned list includes files in nested submodules.
This does not match the behavior of GitChange's AllFiles which uses
git ls-files to find all files.
Implement a new SCM that stops iterating recursively when it
sees a submodule from .gitmodules in the repo root.
Bug: b/323243527
Change-Id: I170d0f1bc4a838acea04779dee3df7fca0bce359
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5648616
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>
Commit-Queue: Gavin Mak <gavinmak@google.com>
