Automatic merge from submit-queue
Add test_list command, to enumerate unit and e2e tests.
This uses go/parser and go/ast to analyze all test files in ~1 second.
It only recognizes a few simple structures that the tests all have, and
modifies a few tests to fit expected structure better.
This is part of an effort to ensure all tests have owners, by having a
verify check to catch new tests being added without an owner.
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