[clang-tidy] fix PR36489 - respect deduced pointer types from auto as well

Summary:
The cppcoreguidelines-pro-bounds-pointer-arithmetic warns on all occassion where
pointer arithmetic is used, but does not check values where the pointer types
is deduced via ``auto``. This patch adjusts this behaviour and solved
PR36489.

Reviewers: alexfh, aaron.ballman, hokein, ilya-biryukov

Reviewed By: alexfh, aaron.ballman

Subscribers: nemanjai, xazax.hun, kbarton, cfe-commits

Differential Revision: https://reviews.llvm.org/D48717

llvm-svn: 337710