This PR integrates `compiletest_rs` as suggested in #5646. I created a new `tests/compiletest` directory which contains separate crates for the tests.
Currently this PR includes `compile-fail` tests for some lints (acutally all except inheritance_integrity, beacuse I'm not sure how to include the dom stuff in a way the `#[dom_struct]` works).
I gathered that there should be more crates for which compiletests make sense and would appreciate any pointers to relevant crates.
Source-Repo: https://github.com/servo/servo
Source-Revision: d574b78313be75f3388123d11354b897598877a3
c8106495a8