Auto merge of #97697 - WaffleLapkin:no_ref_vec, r=WaffleLapkin

Replace `&Vec<_>`s with `&[_]`s

It's generally preferable to use `&[_]` since it's one less indirection and it can be created from types other that `Vec`.

I've left `&Vec` in some locals where it doesn't really matter, in cases where `TypeFoldable` is expected (`TypeFoldable: Clone` so slice can't implement it) and in cases where it's `&TypeAliasThatIsActiallyVec`. Nothing important, really, I was just a little annoyed by `visit_generic_param_vec` :D

r? `@compiler-errors`

Author: bors