Rollup merge of #88894 - FabianWolff:issue-88818, r=estebank

Improve error message for missing trait in trait impl

Fixes #88818. For the following example:
```rust
struct S { }
impl for S { }
```
the current output is:
```
error: missing trait in a trait impl
 --> t1.rs:2:5
  |
2 | impl for S { }
  |     ^
```
With my changes, I get:
```
error: missing trait in a trait impl
 --> t1.rs:2:5
  |
2 | impl for S { }
  |     ^
  |
help: add a trait here
  |
2 | impl Trait for S { }
  |      +++++
help: for an inherent impl, drop this `for`
  |
2 - impl for S { }
2 + impl S { }
  |
```

0 files changed, 0 insertions, 0 deletions