[AArch64][SVE2] Add the SVE2.1 shift-and-narrow instructions

[AArch64][SVE2] Add the SVE2.1 shift-and-narrow instructions

This patch adds the assembly/disassembly for the following instructions:

sqrshrn  : Signed saturating rounding shift right narrow by immediate and interleave
sqrshrun : Signed saturating rounding shift right unsigned narrow by immediate and interleave
uqrshrn  : Unsigned saturating rounding shift right narrow by immediate and interleave

The reference can be found here:
https://developer.arm.com/documentation/ddi0602/2022-09

Differential Revision: https://reviews.llvm.org/D136690