Per the Mainline requirement to setup coverage for APIs used by
modules, we need to add the plugin 'java_api_finder' to ANGLE's
Android.bp to enable the instrumentation.

Bug: b:148987998
Test: Generate Android.bp, verify GoogleANGLE can build in goog/master
Change-Id: Id3d82f18ecb9ff6a57cda4a60f14cd2464dff234
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2145236Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Tim Van Patten <timvp@google.com>