core.sys.windows.winuser: Provide valid GetMonitorInfo overloads

LDC isn't fooled by using the same mangled name for multiple C function
declarations with differing signatures (see DMD bugzilla 15217).

In the MS header, the ...EX structs derive from the non-EX ones, so a
pointer to an EX struct is implicitly converted to a pointer to the base
struct.

Provide extern(D) wrappers performing the explicitly required cast in D.

src/core/sys/windows/winuser.d

@@ -4423,9 +4423,9 @@ int BroadcastSystemMessageW(DWORD, LPDWORD, UINT, WPARAM, LPARAM);
 UINT SendInput(UINT, LPINPUT, int);
 BOOL EnumDisplayMonitors(HDC, LPCRECT, MONITORENUMPROC, LPARAM);
 BOOL GetMonitorInfoA(HMONITOR, LPMONITORINFO);
-BOOL GetMonitorInfoA(HMONITOR, LPMONITORINFOEXA);
+extern(D) BOOL GetMonitorInfoA(HMONITOR m, LPMONITORINFOEXA mi) { return GetMonitorInfoA(m, cast(LPMONITORINFO)mi); }
 BOOL GetMonitorInfoW(HMONITOR, LPMONITORINFO);
-BOOL GetMonitorInfoW(HMONITOR, LPMONITORINFOEXW);
+extern(D) BOOL GetMonitorInfoW(HMONITOR m, LPMONITORINFOEXW mi) { return GetMonitorInfoW(m, cast(LPMONITORINFO)mi); }
 HMONITOR MonitorFromPoint(POINT, DWORD);
 HMONITOR MonitorFromRect(LPCRECT, DWORD);
 HMONITOR MonitorFromWindow(HWND, DWORD);