[docs] improve documentation for misc-const-correctness

Improve the documentation for 'misc-const-correctness' to:

- include better examples
- improve the english
- fix links to other checks that were broken due to the directory-layout changes
- mention the limitation that the check does not run on `C` code.

Addresses #56749, #56958

Reviewed By: njames93

Differential Revision: https://reviews.llvm.org/D132244