Allow multiple solutions in a suggestion

[pietroalbini]

At the moment, rustfix discards all the suggestions with more than one solution. This prevent implementing machine-applicable fixes for unused_lints where multiple sections of the line needs to be removed:

warning: unused imports: `HashMap`, `HashSet`
 --> src/main.rs:2:24
  |
2 | use std::collections::{HashMap, VecDeque, HashSet};
  |                        ^^^^^^^            ^^^^^^^
  |
  = note: #[warn(unused_imports)] on by default
help: remove this
  |
2 | use std::collections::{VecDeque};
  |                       --      --

This patch changes the behavior to allow multiple solutions.

[pietroalbini]

Also removed a test that was checking for this behavior.

r? @killercup

[killercup]

Thanks, this looks good! Can you add a new test with a >1 solutions case?

[pietroalbini]

Ok, changed the test suite to use the cached json instead of calling rustc (since it's not possible to do so until the lint is merged into rustc, which is blocked on this) and added a test.

[killercup]

Thanks!

[zackmdavis]

@pietroalbini @killercup Can we also get a test for multiple distinct suggestions? That is, if I understand correctly, the test added in 4595c3b is using JSON that was generated by calling multipart_suggestion_with_applicability in the compiler (in the open PR rust-lang/rust#56645), but I'm concerned that we want rustfix to handle this differently than JSON generated by calling .span_suggestions_with_applicability (or calling .span_suggestion twice),

(I regret the lack of initiative implied by me leaving this mere comment rather than submitting a PR (as it is written, "patch or STFU"), but I'm afraid I don't have time today.)