Remove test_per_src from ART tests.

Remove test_per_src since it is not supported by atest.
Replace it with gtest_isolate which is transparent to atest,
and which still allows us to run tests in parallel.

The size of test binaries halves (from 1GB to 0.5GB).
Test run-time on host is unchanged.
Test run-time on target is 4x faster (tested on walleye).

Bug: 147819342
Test: m test-art-host-gtest
Test: art/tools/run-gtests.sh
Change-Id: Id295af00d08b24baa2e421b0f3313df0b2e56fe9
18 files changed