Implement constexpr BinaryOperator for vector types

These operations do member-wise versions of the all of the listed
operations.  This patch implements all of the binaryoperators for these
types. Note that the test is required to use codegen as I could not come
up with a good way to validate the values without the array-subscript
operator implemented (which is likely a much more involved change).

Differential Reivision: https://reviews.llvm.org/D79755