base-builder: add script for collecting coverage from run_test.sh

[DavidKorczynski]

Coverage collection based on coverage reports generated from running run_tests.sh can be useful for various things.

To run:

$ python3 infra/helper.py shell zlib --sanitizer=coverage

# Inside the shell
compile && chmod +x /src/run_tests.sh && /src/run_tests.sh && python3 /usr/local/bin/coverage_test_collection.py

The above command will put a HTML report in /out/test-html-generation which can be viewed outside the container environment (ensure permissions are correct on the files).

Sample from zlib:

[DavidKorczynski]

closing in favour of #13740