P3793R2 Better Shifting

[StephanTLavavej]

WG21-P3793R2 Better Shifting

INCREASED feature-test macro, NOTE special interaction with #6328 WG21-P3104R6 Bit Permutations which further increased this:

#define __cpp_lib_bitops 202606L

Added feature-test macro, NOTE special interaction with #6338 WG21-P3772R2 simd Overloads For Bit Permutations which then increased this:

#define __cpp_lib_simd_bitops 202606L

Note: We are not yet accepting PRs for C++29 features.