5684: Semantic highlighting for unsafe union field access r=jonas-schievink a=Nashenas88
This change adds support for unions in inference and lowering, then extends on that to add the unsafe semantic modifier on field access only. The `is_possibly_unsafe` function in `syntax_highlighting.rs` could be extended to support fns and static muts so that their definitions are not highlighted as unsafe, but only their usage.
Also, each commit of this PR updates the tests. By reviewing the files by commit, it's easy to see how the changes in the code affected the tests.
Co-authored-by: Paul Daniel Faria <Nashenas88@users.noreply.github.com>
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