Support SF Symbols images on macOS 11

Extend wxOSXGetSystemImage() and thus wxArtProvider with support for directly
loading the new symbolic images in addition to existing support for named
bundle resources.

This enables usage such as wxArtProvider::GetBitmap("gearshape").

src/osx/carbon/utilscocoa.mm

@@ -183,6 +183,16 @@ wxBitmap wxOSXCreateSystemBitmap(const wxString& name, const wxString &client, c
 WXImage wxOSXGetSystemImage(const wxString& name)
 {
     wxCFStringRef cfname(name);
+
+#if __MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_16
+    if ( WX_IS_MACOS_AVAILABLE(11, 0) )
+    {
+        NSImage *symbol = [NSImage imageWithSystemSymbolName:cfname.AsNSString() accessibilityDescription:nil];
+        if ( symbol )
+            return symbol;
+    }
+#endif
+    
     NSImage* nsimage = [NSImage imageNamed:cfname.AsNSString()];
     return nsimage;
 }