[clang-tidy] Improving bugprone-sizeof-expr check.

Do not warn for "pointer to aggregate" in a `sizeof(A) / sizeof(A[0])`
expression if `A` is an array of pointers. This is the usual way of
calculating the array length even if the array is of pointers.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D91543