Revert "Revert "Switch to Metalava to generate libcore docs""

This reverts commit 1dd1f619.

Reason for revert:
Switch to Metalava to generate libcore docs, attempt 2.

This is the second attempt to merge this CL.
The first attempt failed because it break all robolectric tests.

Tor located the issue that "--exclude-annoations" should not affect runtime annoations in Metalava.

This issue was fixed by go/oag/735473

Test: make RunSettingLibRoboTests -j40
Bug: b/78245848

Change-Id: Icb5e8ced6ebabc14ac9e79202b09af8b5523ff57