9453: Add first-class limits. r=matklad,lnicola a=rbartlensky
Partially fixes#9286.
This introduces a new `Limits` structure which is passed as an input
to `SourceDatabase`. This makes limits accessible almost everywhere in
the code, since most places have a database in scope.
One downside of this approach is that whenever you query limits, you
essentially do an `Arc::clone` which is less than ideal.
Let me know if I missed anything, or would like me to take a different approach!
Co-authored-by: Robert Bartlensky <bartlensky.robert@gmail.com>
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