Add libcore/ojluni/annotations as a source for metalava.

This adds the new annotations (in Java stub format) to the list that
metalava will merge when building stubs.

Bug: 111639530
Test: `make metalava-api-stubs-docs`
Change-Id: I5e73d1276f0602bd14a41f7a64659b1a7b1347cf
1 file changed