[clang-tidy] Add parametercount for readibility-function-size

Summary:
Add an option to function-size to warn about high parameter counts.

This might be relevant for cppcoreguidelines and the safety module as well. Since the safety module is not landed in master already, i did not create an alias, but that can be done later as well.

Reviewers: sbenza, alexfh, hokein

Reviewed By: alexfh, hokein

Subscribers: JDevlieghere

Patch by Jonas Toth!

Differential Revision: https://reviews.llvm.org/D29561

llvm-svn: 296599