COMP: Prefer const pointer when value does not change

The check finds function parameters of a pointer type that could be changed to
point to a constant type instead.

When const is used properly, many mistakes can be avoided. Advantages when
using const properly:
 - prevent unintentional modification of data;
 - get additional warnings such as using uninitialized data;
 - make it easier for developers to see possible side effects.

This check is not strict about constness, it only warns when the constness will
make the function interface safer.