Fix case of <shlwapi.h> includes

Don't use upper-case file names, while MSW itself is case-insensitive, wxMSW
can be also cross-compiled and then the wrong case results in compilation
errors.

Closes #17279.

src/msw/textentry.cpp

@@ -40,7 +40,7 @@
 #endif
 
 #include "wx/msw/wrapwin.h"
-#include <Shlwapi.h>
+#include <shlwapi.h>
 
 #define GetEditHwnd() ((HWND)(GetEditHWND()))
 

src/msw/utilsgui.cpp

@@ -32,7 +32,7 @@
 #include "wx/msw/private.h"     // includes <windows.h>
 
 #include "wx/msw/wrapwin.h"
-#include <Shlwapi.h>
+#include <shlwapi.h>
 
 // ============================================================================
 // implementation