All gtest-based tests should now use add_gtest. Results from these tests
will be surfaced more prominently in GitHub Actions. Before this, it was
hard to find test failures in the log.
Rebasing #1148 on top of current cmake branch
Related to #1047
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Co-authored-by: Bartek Zdanowski <bartek.zdanowski@gmail.com>
Co-authored-by: Joey Parrish <joeyparrish@google.com>