Add support for arrays in performance-implicit-conversion-in-loop

Summary:
Add support for arrays (and structure that use naked pointers for their iterator, like std::array) in performance-implicit-conversion-in-loop

Reviewers: alexfh

Reviewed By: alexfh

Subscribers: cfe-commits

Patch by Alex Pilkiewicz.

Differential Revision: https://reviews.llvm.org/D47945

llvm-svn: 334400