8942: Add `library` semantic token modifier to items from other crates r=arzg a=arzg
Closes#5772.
A lot of code here is pretty repetitive; please let me know if you have any ideas how to improve it, or whether it’s fine as-is.
Side-note: How can I add tests for this? I don’t see a way for the test Rust code in `test_highlighting` to reference other crates to observe the new behaviour.
Co-authored-by: Aramis Razzaghipour <aramisnoah@gmail.com>
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