Put 75% of ART run-tests in `TEST_MAPPING` group `mainline-presubmit`.

Include more ART run-tests into the `mainline-presubmit` test
group. This progressive rollout is to make sure introducing ART
run-tests to this test group won't disturb/break Android presubmits.

Output of `art/test/utils/regen-test-files`:

  $ art/test/utils/regen-test-files
  Generated Blueprint files for 623 ART run-tests out of 927 (67%).
  Generated TEST_MAPPING entries for 376 ART run-tests out of 927 (40%):
    282 tests (75%) in `mainline-presubmit` test group.
    376 tests (100%) in `presubmit` test group.
    0 tests (0%) in `postsubmit` test group.

Test: Rely on TreeHugger presubmits
Bug: 178703264
Bug: 152374989
Change-Id: I947fa6380e09f22dabe3e0b9713e32191cc52e21
2 files changed