Add constructor reference support for attributes

[RemcoSmitsDev]

Hey, while I was trying out this LSP again, I noticed that find all references for a constructor didn't work in combination with attributes. So this PR fixes this by adding a new ClassRefContext option called Attribute, this allows us to do some additional checks for getting all the right references in the case of class attributes.

Here is a video of how works now, vs how it was before (it didn't find any references at all) because the class used in my example the symfony Group class attribute is never normally instantiated using new Group.

Note for the reviewer: A part of this change was assistet with AI because I don't know the code that good.
So let me know if you want me to make any changes!

Screen.Recording.2026-06-13.at.20.24.52.mov

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 89.10256% with 17 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/references/mod.rs	89.47%	16 Missing ⚠️
src/diagnostics/invalid_class_kind.rs	50.00%	1 Missing ⚠️

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[AJenbo]

Thanks for working on this