Searching for an ident should take aliasing into account

[Xanewok]

Originally created by @nrc (rust-dev-tools/rls-analysis#137):

e.g., if there is use foo as bar, then we should be able to search for bar. Currently this would give no results.

[Xanewok]

In general goto-defs/refs work for:

struct Struct { inner: () }
use Struct as MySuperStruct;

fn main() {
    let a = Struct { inner: () };
    let a = MySuperStruct { inner: () };
}

But workspace symbols only return Struct - I assume we'd like it to return the alias as well.