Compiler type trait optimizations

[StephanTLavavej]

This ports @xiangfan-ms's MSVC-PR-360974, which was merged on 2021-10-29 but we forgot to mirror it.

Xiang optimized the MSVC compiler front-end to recognize type_identity_t and _Identity_t, which became heavily used after we merged #2032 implementing P1518R2 Stop Overconstraining Allocators In Container Deduction Guides.

As part of this work, our internal aliases _Identity_t and _Remove_cvref_t need to be marked with the attribute _MSVC_KNOWN_SEMANTICS:

STL/stl/inc/yvals_core.h

Lines 424 to 434 in 1801934

	// Determine if we should use [[msvc::known_semantics]] to communicate to the compiler
	// that certain type trait specializations have the standard-mandated semantics
	#ifndef __has_cpp_attribute
	#define _MSVC_KNOWN_SEMANTICS
	#elif defined(__CUDACC__) // TRANSITION, CUDA - warning: attribute namespace "msvc" is unrecognized
	#define _MSVC_KNOWN_SEMANTICS
	#elif __has_cpp_attribute(msvc::known_semantics)
	#define _MSVC_KNOWN_SEMANTICS [[msvc::known_semantics]]
	#else
	#define _MSVC_KNOWN_SEMANTICS
	#endif