remove wxMSW-specific FindSuitableParent() and use GetParentForModalDialog() everywhere; extend it with additional checks and remove redundant ones elsewhere

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@60559 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/dialog.h

@@ -91,7 +91,7 @@ public:
     int GetEscapeId() const { return m_escapeId; }
 
     // Returns the parent to use for modal dialogs if the user did not specify it
-    // explicitly
+    // explicitly. If parent argument is NULL, use GetParent() by default.
     wxWindow *GetParentForModalDialog(wxWindow *parent = NULL) const;
 
 #if wxUSE_STATTEXT // && wxUSE_TEXTCTRL
@@ -211,6 +211,10 @@ private:
     // common part of all ctors
     void Init();
 
+    // helper of GetParentForModalDialog(): returns the passed in window if it
+    // can be used as our parent or NULL if it can't
+    wxWindow *CheckIfCanBeUsedAsParent(wxWindow *parent) const;
+
     // handle Esc key presses
     void OnCharHook(wxKeyEvent& event);