This adds `./mach test-tidy --stylo`, which turns off the usage of git to search for files to check (fixes #14855), and also turns off the wpt lint, making it possible to run tidy in a stylo tree. r? @jdm @wafflespeanut cc @bzbarsky Source-Repo: https://github.com/servo/servo Source-Revision: 9eaf96b73716450caba5e85b9c5d3622242f2608