[AArch64][NFC] Refactor NEON, SVE and SME classes and multiclasses fo… (#68800)

…r the assembly disassembly

This NFC patch refactors the assembly/disassembly class and multiclass
in the AArch64 backend to receive a new 2023/09 AArch64[1] ISA release.
The encoding for the 2023 instructions re-uses encoding blocks from
previous assembly/disassembly instructions.
The refactoring makes the class and multiclass for assembly/disassembly
generic so it can be used to describe the instructions for the new ISA.

[1]https://developer.arm.com/documentation/ddi0602/2023-09