AArch64: Add SVE2 path for convertSequences_noRepcodes

AArch64: Add SVE2 path for convertSequences_noRepcodes

Add an 8-way vector length agnostic (VLA) SVE2 code path for
convertSequences_noRepcodes. It works with any SVE vector length.

Relative performance to GCC-13 using: `./fullbench -b18 -l5 enwik5`

               Neon      SVE2
Neoverse-V2   before     after    uplift
GCC-13:      100.000%  103.209%   1.032x
GCC-14:      100.309%  134.872%   1.344x
GCC-15:      100.355%  134.827%   1.343x
Clang-18:    123.614%  128.565%   1.040x
Clang-19:    123.587%  132.984%   1.076x
Clang-20:    123.629%  133.023%   1.075x

               Neon      SVE2
Cortex-A720   before     after    uplift
GCC-13:      100.000%  116.032%   1.160x
GCC-14:       99.700%  116.648%   1.169x
GCC-15:      100.354%  117.047%   1.166x
Clang-18:    100.447%  116.762%   1.162x
Clang-19:    100.454%  116.627%   1.160x
Clang-20:    100.452%  116.649%   1.161x