Rollup merge of #95970 - WaffleLapkin:nicer_trait_suggestions, r=compiler-errors

Rollup merge of #95970 - WaffleLapkin:nicer_trait_suggestions, r=compiler-errors

Fix suggestions in case of `T:` bounds

This PR fixes a corner case in `suggest_constraining_type_params` that was causing incorrect suggestions.

For the following functions:
```rust
fn a<T:>(t: T) { [t, t]; }
fn b<T>(t: T) where T: { [t, t]; }
```

We previously suggested the following:
```text
...
help: consider restricting type parameter `T`
  |
1 | fn a<T: Copy:>(t: T) { [t, t]; }
  |       ++++++
...
help: consider further restricting this bound
  |
2 | fn b<T>(t: T) where T: + Copy { [t, t]; }
  |                        ++++++
```

Note that neither `T: Copy:` not `where T: + Copy` is a correct bound.

With this commit the suggestions are correct:
```text
...
help: consider restricting type parameter `T`
  |
1 | fn a<T: Copy>(t: T) { [t, t]; }
  |         ++++
...
help: consider further restricting this bound
  |
2 | fn b<T>(t: T) where T: Copy { [t, t]; }
  |                        ++++
```

r? `@compiler-errors`

I've tried fixing #95898 here too, but got too confused with how `suggest_traits_to_import` works and what it does :sweat_smile: