Compile fail tests for bevy_reflect

This crate is separate from bevy_reflect and not part of the Bevy workspace in order to not fail crater tests for Bevy. The tests assert on the exact compiler errors and can easily fail for new Rust versions due to updated compiler errors (e.g. changes in spans).

The CI workflow executes these tests on the stable rust toolchain (see tools/ci).

For information on writing tests see compile_fail_utils/README.md.