<locale>: Repair std::collate<unsigned short>

[muellerj2]

This repairs collate<unsigned short> by adding two missing unsigned short specializations for _LStrcoll and _LStrxfrm when wchar_t is a native type. Fixes #5236.

There are similar specializations for a few functions in <xlocale>. I guess _LStrcoll and _LStrxfrm were missed because they are located in a different header.

Since collate is the only user of these functions, I also moved them from <xlocinfo> to <locale> just above collate.

As for why this also fixes collate<wchar_t> = collate<unsigned short> under non-native wchar_t when linking to the DLL, this is because the the locale facets are constructed in the DLL here:

STL/stl/src/wlocale.cpp

Lines 58 to 88 in f2a2933

	// moved from locale to ease subsetting
	using _Tu1 = ctype<unsigned short>;
	using _Tu2 = num_get<unsigned short>;
	using _Tu3 = num_put<unsigned short>;
	using _Tu4 = numpunct<unsigned short>;
	using _Tu5 = collate<unsigned short>;
	using _Tu6 = messages<unsigned short>;
	using _Tu7 = money_get<unsigned short>;
	using _Tu8 = money_put<unsigned short>;
	using _Tu9 = moneypunct<unsigned short, false>;
	using _Tu10 = moneypunct<unsigned short, true>;
	using _Tu11 = time_get<unsigned short>;
	using _Tu12 = time_put<unsigned short>;
	using _Tu13 = codecvt<unsigned short, char, _Mbstatet>;
	void __CLRCALL_OR_CDECL locale::_Locimp::_Makeushloc(const _Locinfo& lobj, locale::category cat, _Locimp* ptrimp,
	const locale* ptrloc) { // setup wide part of a new locale
	ADDFAC(_Tu1, cat, ptrimp, ptrloc);
	ADDFAC(_Tu2, cat, ptrimp, ptrloc);
	ADDFAC(_Tu3, cat, ptrimp, ptrloc);
	ADDFAC(_Tu4, cat, ptrimp, ptrloc);
	ADDFAC(_Tu5, cat, ptrimp, ptrloc);
	ADDFAC(_Tu6, cat, ptrimp, ptrloc);
	ADDFAC(_Tu7, cat, ptrimp, ptrloc);
	ADDFAC(_Tu8, cat, ptrimp, ptrloc);
	ADDFAC(_Tu9, cat, ptrimp, ptrloc);
	ADDFAC(_Tu10, cat, ptrimp, ptrloc);
	ADDFAC(_Tu11, cat, ptrimp, ptrloc);
	ADDFAC(_Tu12, cat, ptrimp, ptrloc);
	ADDFAC(_Tu13, cat, ptrimp, ptrloc);
	}

Thus, collate's virtual functions originate from the DLL as well. These virtual functions call _LStrcoll and _LStrxfrm, but the specializations for unsigned short were missing since the DLL is built with native wchar_t.

The setup of the new test is a bit wild, but it's the best I could come up with:

• Since we should test this under native wchar_t, we have to make collate<unsigned short> well-defined by setting _ENFORCE_LOCALE_SPECIALIZATIONS to 0.
• We have to skip collate::transform() tests when there is IDL mismatch between TU and linked DLL.
• When linking to the DLL, we have to define collate<unsigned short>::id. I tried defining __FORCE_INSTANCE instead (which is used to the same effect during the DLL build), but this results in several warnings-turned-errors in other facets. So it's either this or suppressing more warnings in STL headers.