Function safe_arch::bit_zero_high_index_u64

#[must_use]pub fn bit_zero_high_index_u64(a: u64, index: u32) -> u64

This is supported with target feature bmi2 only.

Zero out all high bits in a u64 starting at the index given.

assert_eq!(bit_zero_high_index_u64(0b1111, 0), 0b0000);
assert_eq!(bit_zero_high_index_u64(0b1111, 1), 0b0001);
assert_eq!(bit_zero_high_index_u64(0b1111, 2), 0b0011);
assert_eq!(bit_zero_high_index_u64(0b1111, 3), 0b0111);