Merge #4596

4596: Strip leading underscores of argument names in function/method r=matklad a=kuy

Closes #4510 

### Goal

When I select a function/method from completions, I get a snippet that doesn't contain leading underscores of argument names.

### Solution

- Option 1: All signatures don't contain underscores
- Option 2: Keep same signature, but inserted snippet doesn't contain underscores

I choose Option 2 because I think that leading underscores is a part of "signature". Users should get correct signatures. On the other hand, trimming underscores is an assist by IDE.

### Other impls.

rls: Complete argument names with underscores (same as actual ra)
IntelliJ Rust: Doesn't complete argument names
VSCode (TypeScript): Doesn't complete argument names

### Working example

![Screen Shot 2020-05-25 at 0 03 21](https://user-images.githubusercontent.com/151614/82757771-a05e5b80-9e1d-11ea-9dbc-1263c960e2ae.png)


Co-authored-by: Yuki Kodama <[email protected]>

0 files changed, 0 insertions, 0 deletions