This gives some flexibility to embedders.
Currently, embedders have to build a binary for each test file.
After this CL, embedders can still choose to have a binary for each test
file, by linking each test file with a googletest target that includes
main() (usually "gtest_main"). Embedders can also choose to build a
single binary for almost all test files, and link with a googletest
target that includes main(). The latter is more convenient for projects
that have very few test binaries, like Chromium.
PiperOrigin-RevId: 419470798
Use clang-format to correct formatting to be in agreement with the [Google C++ Style Guide](https://google.github.io/styleguide/cppguide.html). Doing this simplifies the process of accepting changes. Also fixed a few warnings flagged by clang-tidy.
PiperOrigin-RevId: 246350737
