Function safe_arch::cast_to_m128d_from_m128

#[must_use]pub fn cast_to_m128d_from_m128(a: m128) -> m128d

This is supported with target feature sse2 only.

Bit-preserving cast to m128d from m128

let a = m128::from_array([1.0, 2.0, 3.0, 4.0]);
let c: [u64; 2] = cast_to_m128d_from_m128(a).to_bits();
assert_eq!(c, [0x400000003F800000, 0x4080000040400000]);