[ADT][NFC] Add extra typedefs to `ArrayRef` and `MutableArrayRef`

* `value_type`
* `pointer`
* `const_pointer`
* `reference`
* `const_reference`
* `const_reverse_iterator`
* `size_type`
* `difference_type`

It makes `ArrayRef` and `MutableArrayRef` types fully compliant with STL Container concept.

Reviewed By: lattner, courbet

Differential Revision: https://reviews.llvm.org/D95611