[llvm] [NFCI][LLVM] Adopt `ArrayRef::consume_front()` in a few places (PR #146793)

[Jakub Kuderski via llvm-commits]

kuhar wrote:

I'm -1 on the renaming -- `pop_*_val` change the underlying container contents, whereas `consume_` only adjust pointers. This is consistent with the naming in `StringRef`.

https://github.com/llvm/llvm-project/pull/146793