AArch64: Add Neon path for convertSequences_noRepcodes

AArch64: Add Neon path for convertSequences_noRepcodes

Add a 4-way Neon implementation for the convertSequences_noRepcodes
function. Remove 'static' keywords from all of its implementations to
be able to add unit tests.

Relative performance to Clang-18 using: `./fullbench -b18 -l5 enwik5`

Neoverse-V2   before     after
Clang-18:    100.000%  311.703%
Clang-19:    100.191%  311.714%
Clang-20:    100.181%  311.723%
GCC-13:      107.520%  252.309%
GCC-14:      107.652%  253.158%
GCC-15:      107.674%  253.168%

Cortex-A720   before     after
Clang-18:    100.000%  204.512%
Clang-19:    102.825%  204.600%
Clang-20:    102.807%  204.558%
GCC-13:      110.668%  203.594%
GCC-14:      110.684%  203.978%
GCC-15:      102.864%  204.299%

Co-authored by, Thomas Daubney <Thomas.Daubney@arm.com>