Add diagnostic for incorrect `pub (restriction)`
Given the following statement
```rust
pub (a) fn afn() {}
```
Provide the following diagnostic:
```rust
error: incorrect restriction in `pub`
--> file.rs:15:1
|
15 | pub (a) fn afn() {}
| ^^^
|
= help: some valid visibility restrictions are:
`pub(crate)`: visible only on the current crate
`pub(super)`: visible only in the current module's parent
`pub(in path::to::module)`: visible only on the specified path
help: to make this visible only to module `a`, add `in` before the path:
| pub (in a) fn afn() {}
```
Follow up to #40340, fix#40599, cc #32409.
640dbbdd3a