Rename DOMPatchStatus -> Patch

(It does a lot more than reflecting the status)

Also make Patch a ThreadableLoaderClient instead of using an internal
class for it, as it removes some broilerplate.

Bug: 431374376
Change-Id: I7dbd276f4cb9b00b41520d9d5dd5c7447bc3cdec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6818499
Commit-Queue: Noam Rosenthal <nrosenthal@google.com>
Reviewed-by: Mason Freed <masonf@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1497409}