3359: Remove AnalysisHost::type_of r=matklad a=edwin0cheng
This PR remove ` AnalysisHost::type_of` (It is subsume by hover now) and use `Semantics::type_of_x` to infer the type inside `hover` directly.
And this also solved a bug : Right now hovering on a string literal inside a macro will show up a `&str` popup correctly. (Except if that involved builtin macro, e.g. `println`)
Co-authored-by: Edwin Cheng <edwin0cheng@gmail.com>