Much faster prompt processing for I-quants (ARM_NEON)

[ikawrakow]

It is time to give some attention to the ARM_NEON back-end, which has fallen behind quite a bit.

This PR corresponds to PRs #531, #533, #534, #546, #549, and applies the on-the-fly repacking technique to i-quants (IQ2_XXS, IQ2_XS, IQ2_S, IQ3_XXS, IQ3_S) for the ARM_NEON implementation.

Here is a PP-512 performance comparison between the main branch and this PR for LlaMA-3.1-8B-Instruct on M2-Max

type	t/s (main)	t/s (PR)	Speedup
IQ2_XXS	55.79	167.55	3.003
IQ2_XS	46.40	166.65	3.592
IQ2_S	42.75	166.83	3.903
IQ3_XXS	51.84	165.56	3.194
IQ3_S	46.02	162.03	3.521

At this point i- and IQK quants are the top tier quants for prompt processing speed on ARM_NEON.