vcam_dataplane builds CoreMedia sample buffers, format descriptions and
pixel buffers from the shared vcam frame for both camera hooks. It is
not linked into either hook yet; the third-party client support in #478
is its first user. `make test-vcam-dataplane` runs its 124 host checks,
and CI now runs it with the loader link tests.
Ported from #477 into VPhoneGuestComponents/VCamDataPlane.
Co-authored-by: Alec Armbruster <35377827+alectrocute@users.noreply.github.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
