Revert "Revert "Make Metalava checkapi a seperate run.""

This reverts commit ec716b41.

Reason for revert:
This is second attempt for Make Metalava checkapi a seperate run.

The first attept didn't work since Metalava also need sources,
classpath, and etc, not like how old Doclava apicheck works.

Test: cherry-pick go/ag/4832335 in internal master, and do 'm clean && m
-j checkapi', it failed with erros which is expected.
Bug: b/113126618, b/113131828

Change-Id: I664b7838d15615905a2e798b1df832218031dfe7