<xmemory>: some std::allocator member functions still need to be removed in C++20

[mnatsuhara]

std::allocator member functions address, max_size, construct, and destroy, should be removed in C++20 mode according to WG21-P0619. Most of the removals in this paper were completed by GH-380, but these seem to have been missed.

[StephanTLavavej]

Removing the cxx20 label which tracks top-level features and controls the Status Chart (when it appears on issues, unlike PRs).

This will probably have some amount of source-breaking impact, but that should be mitigated by:

• These were deprecated in C++17 and we've been emitting warnings
• The STL itself should always be going through allocator_traits (and indeed we had to internally suppress deprecation warnings, because allocator_traits will use these member functions when present), so it should auto-adapt to the member functions vanishing
• A fine-grained escape hatch connected to our coarse-grained escape hatch will allow projects to opt-out of the removal, if they were previously suppressing or ignoring the deprecation warning

The escape hatch system is:

STL/stl/inc/yvals_core.h

Lines 1012 to 1047 in 9959929

	// P0619R4 Removing C++17-Deprecated Features
	#ifndef _HAS_FEATURES_REMOVED_IN_CXX20
	#define _HAS_FEATURES_REMOVED_IN_CXX20 (!_HAS_CXX20)
	#endif // _HAS_FEATURES_REMOVED_IN_CXX20
	#ifndef _HAS_DEPRECATED_ADAPTOR_TYPEDEFS
	#define _HAS_DEPRECATED_ADAPTOR_TYPEDEFS (_HAS_FEATURES_REMOVED_IN_CXX20)
	#endif // _HAS_DEPRECATED_ADAPTOR_TYPEDEFS
	#ifndef _HAS_DEPRECATED_IS_LITERAL_TYPE
	#define _HAS_DEPRECATED_IS_LITERAL_TYPE (_HAS_FEATURES_REMOVED_IN_CXX20)
	#endif // _HAS_DEPRECATED_IS_LITERAL_TYPE
	#ifndef _HAS_DEPRECATED_NEGATORS
	#define _HAS_DEPRECATED_NEGATORS (_HAS_FEATURES_REMOVED_IN_CXX20)
	#endif // _HAS_DEPRECATED_NEGATORS
	#ifndef _HAS_DEPRECATED_RAW_STORAGE_ITERATOR
	#define _HAS_DEPRECATED_RAW_STORAGE_ITERATOR (_HAS_FEATURES_REMOVED_IN_CXX20)
	#endif // _HAS_DEPRECATED_RAW_STORAGE_ITERATOR
	#ifndef _HAS_DEPRECATED_RESULT_OF
	#define _HAS_DEPRECATED_RESULT_OF (_HAS_FEATURES_REMOVED_IN_CXX20)
	#endif // _HAS_DEPRECATED_RESULT_OF
	#ifndef _HAS_DEPRECATED_SHARED_PTR_UNIQUE
	#define _HAS_DEPRECATED_SHARED_PTR_UNIQUE (_HAS_FEATURES_REMOVED_IN_CXX20)
	#endif // _HAS_DEPRECATED_SHARED_PTR_UNIQUE
	#ifndef _HAS_DEPRECATED_TEMPORARY_BUFFER
	#define _HAS_DEPRECATED_TEMPORARY_BUFFER (_HAS_FEATURES_REMOVED_IN_CXX20)
	#endif // _HAS_DEPRECATED_TEMPORARY_BUFFER
	#ifndef _HAS_DEPRECATED_UNCAUGHT_EXCEPTION
	#define _HAS_DEPRECATED_UNCAUGHT_EXCEPTION (_HAS_FEATURES_REMOVED_IN_CXX20)
	#endif // _HAS_DEPRECATED_UNCAUGHT_EXCEPTION