Fix filesystem::weakly_canonical() on Win11 24H2

[StephanTLavavej]

We have a regression test for DevCom-538510 (internal VSO-850856) "std::filesystem::weakly_canonical erroneously throws an exception":

STL/tests/std/tests/P0218R1_filesystem/test.cpp

Lines 3233 to 3237 in ecbc1ef

	// Also test VSO-850856
	// "std::filesystem::weakly_canonical should not throw an exception when a prefix is an existing file"
	const path fileWithSuffix = meow_txt.native() + L"/";
	const path weaklyCanonicalFileWithSuffix = weakly_canonical(fileWithSuffix); // this should not throw
	assert(weaklyCanonicalFileWithSuffix.native().back() == L'\\');

This has regressed on the upcoming Win11 24H2, where we throw an exception (again). The relevant code is:

STL/stl/inc/filesystem

Lines 4127 to 4144 in ecbc1ef

	_EXPORT_STD _NODISCARD inline path weakly_canonical(const path& _Input, error_code& _Ec) {
	// eventually calls GetFinalPathNameByHandleW
	_Ec.clear(); // for exception safety
	path _Temp;
	{
	const auto _Err = _Canonical(_Temp, _Input.native());
	if (_Err == __std_win_error::_Success) {
	return _Temp;
	}
	if (!__std_is_file_not_found(_Err)) {
	_Ec = _Make_ec(_Err);
	return {};
	}
	}

After calling _Canonical(), anything other than _Err == __std_win_error::_Success or __std_is_file_not_found(_Err) is considered a hard error (which will cause the non-error_code overload to throw a filesystem_error).

In current OSes, the fileWithSuffix scenario results in _Invalid_name here. (Locally verified on Win11 23H2. Presumably we get the same behavior in the GitHub PR/CI system running Server 2022 21H2, although I didn't verify that.)

In Win11 24H2, we get _Directory_name_is_invalid, which isn't recognized by __std_is_file_not_found. 💥

The fix is backwards-compatible and a simple one-liner: add this error code enumerator to the list of synonyms that __std_is_file_not_found recognizes. The plain meaning of _Directory_name_is_invalid is clearly a subset of _Invalid_name.

I've manually verified this (with significant but perhaps not surprising logistical difficulty) in an Azure VM with Win11 24H2. Regular test coverage will be provided by the MSVC-internal test harness (which is how we found this), and eventually by the GitHub test harness once Server 2025 24H2 is officially released.

Additionally, this uncaught exception from a non-error_code overload manifested itself as an abort() with no useful logs. To aid in future investigations, I'm including a simple change to the filesystem test. Now, we wrap the whole test in try ... catch and print the contents of any exception before failing.

[StephanTLavavej]

Overriding policy as @zacklj89 approved the internal mirror MSVC-PR-566203.