Putting t.Parallel() in each test makes them run in parallel.
Additional t.Parallel() could be added to each subtest, although
that requires making a local copy of the loop variable for
table driven tests.
Test: m checkbuild
Change-Id: I5d9869ead441093f4d7c5757f2447385333a95a4
This removes ambiguity for developers with the 'stem' property.
Bug: 159064919
Test: New Soong test; error is produced if this property is undefined.
Change-Id: I790fbcfa6cd7dbf6df63b5cf5c22983426ec072e