Initialize MediaProjection API in ScreenCapture code

This CL adds the initialization of the MediaProjection API in the screen
capture code. Doing this involves defining the threading model used by
and between the C++ and Java sides of the implementation. This CL also
handles OS side initiated stopping of sharing via the MediaProjection
API callback.

Bug: 352187279
Test: CQ
Change-Id: I41365fe1c20949b498eb9efaded1f9833be0eb28
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6579089
Reviewed-by: David Trainor <dtrainor@chromium.org>
Reviewed-by: Jordan Bayles <jophba@chromium.org>
Commit-Queue: Eliot Courtney <edcourtney@chromium.org>
Reviewed-by: Calder Kitagawa <ckitagawa@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1471093}