This patch refactors the generate_test_report script, namely turning it
into a proper library, and pulling the script/unittests out into
separate files, as is standard with most python scripts. The main
purpose of this is to enable reusing the library for the new Github
premerge.
Reviewers: tstellar, DavidSpickett, Keenuts, lnihlen
Reviewed By: DavidSpickett
Pull Request: https://github.com/llvm/llvm-project/pull/133196
