[clang-tidy] Add the abseil-duration-comparison check

Summary:
This check finds instances where Duration values are being converted to a numeric value in a comparison expression, and suggests that the conversion happen on the other side of the expression to a Duration.  See documentation for examples.

This also shuffles some code around so that the new check may perform in sone step simplifications also caught by other checks.

Patch by hwright.

Reviewers: aaron.ballman, JonasToth, alexfh, hokein

Reviewed By: JonasToth

Subscribers: sammccall, Eugene.Zelenko, xazax.hun, cfe-commits, mgorny

Tags: #clang-tools-extra

Differential Revision: https://reviews.llvm.org/D54737

llvm-svn: 348161