Type inference fails with local 'use Trait', but works with top-level one

[Vlad-Shcherbina]

To reproduce

1. Open the following program in VSCode:

   // [dependencies]
   // rand = "0.7"
   
   use rand::seq::SliceRandom;
   fn main() {
       let x = [1].choose(&mut rand::thread_rng());
   }

2. Mouse hover over "x".
3. Now change change the program to

   fn main() {
       use rand::seq::SliceRandom;
       let x = [1].choose(&mut rand::thread_rng());
   }

4. Mouse hover over "x" again.

Expected result

In both cases x: Option<&i32>.

Actual result

In the first case x: Option<&i32>, in the second x: {unknown}.

rust-analyzer version: 2020-05-25 (fbb8b88)

[flodiebold]

Duplicate of #1165.