[clang-tidy] new check: bugprone-branch-clone

Summary:
Implement a check for detecting if/else if/else chains where two or more
branches are Type I clones of each other (that is, they contain identical code)
and for detecting switch statements where two or more consecutive branches are
Type I clones of each other.

Patch by donat.nagy.

Reviewers: alexfh, hokein, aaron.ballman, JonasToth

Reviewed By: JonasToth

Subscribers: MTC, lebedev.ri, whisperity, xazax.hun, Eugene.Zelenko, mgorny, rnkovacs, dkrupp, Szelethus, gamesh411, cfe-commits

Tags: #clang-tools-extra

Differential Revision: https://reviews.llvm.org/D54757

llvm-svn: 348343