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

[via cfe-commits]

https://github.com/Sirraide commented:

In addition to what I’ve pointed out below, there are a few more things to be done:
- This needs a release note (in `clang/docs/ReleaseNotes.rst`, probably under the ‘Improvements to Clang’s Diagnostics’ section).
- I find it hard to believe that the test you added is the only thing affected by this; it’s very likely that there are other tests that are failing now because you also need to add the diagnostic there; please run the Clang test suite locally (e.g. `ninja check-clang` if you’re using Ninja as your generator) and fix any tests that this is probably breaking.
- Some more tests, including tests involving templates, would also be a good idea.

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