[blink/WTF] Use base::Lock for WTF::RecursiveMutex

This layers a recursive mutex on top of a non-recursive one
(i.e. base::Lock). It is possibly a tad less efficient than a native
recursive mutex implementation, but the difference is likely extremely
small, as the underlying implementation is similar inside e.g. pthread.

The upside is that after this CL, there is no custom mutex code in blink
anymore.

Bug: 856641, 1290281
Change-Id: I816b9f2788c5457691ffe9908444ded8cd385665
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3480638
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Benoit Lize <lizeb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#975070}