[Clang][AArch64][SVE] Add shift operators for SVE vector types

This patch enables shift operators on SVE vector types, as well as
supporting vector-scalar shift operations.
Shifts by a scalar that is wider than the contained type in the
vector are permitted but as in the C standard if the value is larger
than the width of the type the behavior is undefined.

Differential Revision: https://reviews.llvm.org/D123303