Calling `is_file_open` degrades current query to durability LOW

[MichaReiser]

We noticed in astral-sh/ruff#17463 (comment) that calling is_file_open degrades the durability of otherwise MEDIUM or HIGH durability queries to LOW because the Project::open_files_set and Project::files fields have durability LOW.

What this means is that we degrade the durability of type inference and semantic index queries to LOW if they have any type checking or semantic syntax errors. Which is unfortunate, because it requires that Salsa can't use the fast-path to mark the queries as "up-to-date" after a revision change.

To some extend, this problem is similar to the one we experienced in the module resolver where module resolution first tries first-party files (that have a low durability) and only then tests for third party files.

The easiest solution is to change is_file_open to early return for vendored paths and system paths that aren't subpaths of the project directory.

[MichaReiser]

I think what we could do here now is to call IncludeExcludeFilter::matches_file before testing if the file is in the open_files_set. This should give us a very low false positive rate.

The only thing we may need to investigate is if we can use a prefix filter for ExcludeFilter to avoid traversing all ancestors to determine if the file is excluded (similar to what we do in IncludeFitler). Instead, the method would return early if no prefix matcher matches. We still have to visit all ancestors if any prefix matcher matches because of negated patterns.