Switch car-lib over from doclava to metalava

The platform API files are about to switch to signature file format
v2, which doclava cannot parse, so updating this build to using API
check via metalava instead of doclava.

Note: Metalava checks for additional API and docs problems which
doclava did not; some of these are errors which would fail the
build. Therefore, we turn off these warnings until the source
code is fixed.

Test: make docs
Change-Id: Ic66e24c0af5794f4136d5680ff83d0171ea01af2
Exempt-From-Owner-Approval: Large-scale tooling change
Merged-In: Ib7cab01e85e7032ffbc7cf03771a59b8f2bfd46d
2 files changed