metal : implement q5_0 and q5_1 kernels (#3648)
* metal : implement dequantize_q5_0
* metal : block_q_n_dot_y for block_q5_0 (broken)
* metal : revert unnecessary change
* metal : implement dequantize_q5_1
* metal : block_q_n_dot_y for q5_1 (broken)
* metal : fix block_q_n_dot_y
* minor : spaces / formatting
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Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>
