x86: use simd::intrinsics for bitshifts

[okaneco]

• Use intrinsics in sse2, avx2, avx512f, and avx512bw
• Mark intrinsics and tests that call these functions as const

Nothing notable about the implementation.

Intrinsics take count as the shift argument with the shift being a u64 in the low 64-bits of an __m128i. The shift amount must be less than the bit width of the type being shifted.

[rustbot]

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