[clang-tidy] implement new check 'misc-const-correctness' to add 'const' to unmodified variables

This patch connects the check for const-correctness with the new general
utility to add `const` to variables.
The code-transformation is only done, if the detected variable for const-ness
is not part of a group-declaration.

The check allows to control multiple facets of adding `const`, e.g. if pointers themself should be
marked as `const` if they are not changed.

Reviewed By: njames93

Differential Revision: https://reviews.llvm.org/D54943