[clang] [clang] Fix-it hint for `++this` -> `++*this` when deref is modifiable (PR #94159)

[via cfe-commits]

https://github.com/Sirraide commented:

The implementation looks fine, but a few more tests involving templates would be nice to see what this does with dependent types, e.g.

```c++
template <typename T>
void f(T& t) {
    ++t;
}

void g() {
    int* a;
    int* const b = a;
    const int* const c = a;
    f(a); // Ok.
    f(b); // Error and fixit.
    f(c); // Error, but no fixit.
}
```

I’d expect an error to be reported at instantiation time only; I doubt that there will be any complications here, but more tests are never a bad idea.

https://github.com/llvm/llvm-project/pull/94159