Merge #9800

9800: feat: Include suggested replacement in diagnostics r=jonas-schievink a=jonas-schievink

rustc renders the diagnostic text for suggestions by including the suggested replacement at the end (`` help: a function with a similar name exists: `boo` ``), but the emitted JSON diagnostic does not include this in the message. This causes our diagnostics to lack some useful info, so this PR fixes that by appending any suggested replacements to the message.

Fixes https://github.com/rust-analyzer/rust-analyzer/issues/9797

Before:
![screenshot-2021-08-06-15:54:19](https://user-images.githubusercontent.com/1786438/128521003-105a43a3-e386-4afc-9d5c-7806631f53d7.png)

After:
![screenshot-2021-08-06-15:53:16](https://user-images.githubusercontent.com/1786438/128521022-c16e0967-6cc6-410d-917d-5db5cfbb96be.png)

bors r+

Co-authored-by: Jonas Schievink <jonasschievink@gmail.com>