Merge branch 'msw-popup'

Reimplement wxPopupWindow using WS_POPUP instead of WS_CHILD window in
wxMSW as the new approach allows using the controls inside the popup
normally, unlike the old one.

See https://github.com/wxWidgets/wxWidgets/pull/986

Closes #18243.

interface/wx/popupwin.h

@@ -84,10 +84,10 @@ public:
     /**
         Popup the window (this will show it too).
 
-        If @a winFocus is non-@NULL, it will be kept focused while this window
-        is shown, otherwise this window itself will receive focus. In any case,
-        the popup will disappear automatically if it loses focus because of a
-        user action.
+        If @a focus is non-@NULL, it will be kept focused while this window
+        is shown if supported by the current platform, otherwise the popup
+        itself will receive focus. In any case, the popup will disappear
+        automatically if it loses focus because of a user action.
 
         @see Dismiss()
     */