Test formatters do not generate test file path information

[yqiu24]

Problem

The output of the test formatters --format=junit and --format=json don't include the source test file information, which is available in the source_file property of TestDesc (here). This information would help us with test parsing in CI and better ownership attribution (based on file owners).

Note: For --format=json, this is printed with the --list option, but not in the actual test result event.