`<filesystem>`: Resize files in a better way

[AlexGuteniev]

Currently <filesystem> and its experimental ancestor use SetFilePointerEx + SetEndOfFile:

STL/stl/src/filesys.cpp

Lines 418 to 430 in 17fde2c

	_FS_DLL int __CLRCALL_PURE_OR_CDECL _Resize(const wchar_t* _Fname, uintmax_t _Newsize) { // change file size
	bool _Ok = false;
	HANDLE _Handle = _FilesysOpenFile(_Fname, FILE_GENERIC_WRITE, 0);
	if (_Handle != INVALID_HANDLE_VALUE) { // set file pointer to new size and trim
	LARGE_INTEGER _Large;
	_Large.QuadPart = _Newsize;
	_Ok = SetFilePointerEx(_Handle, _Large, nullptr, FILE_BEGIN) != 0 && SetEndOfFile(_Handle) != 0;
	CloseHandle(_Handle);
	}
	return _Ok ? 0 : GetLastError();
	}

STL/stl/src/filesystem.cpp

Lines 696 to 702 in 17fde2c

	LARGE_INTEGER _Large;
	_Large.QuadPart = _New_size;
	if (SetFilePointerEx(_Handle._Get(), _Large, nullptr, FILE_BEGIN) == 0 || SetEndOfFile(_Handle._Get()) == 0) {
	return __std_win_error{GetLastError()};
	}
	return __std_win_error::_Success;

The modern way, which is supported starting in Windows Vista is SetFileInformationByHandle with FILE_END_OF_FILE_INFO.
It would make fewer kernel calls and cleaner code.

Probably should wait till #2766 is handled to avoid conflicts.