Factor out wxWidgetCocoaImpl::GetViewWithText()

Extract this function from wxWidgetCocoaImpl::SetFont() to allow its
reuse.

No changes, this is a pure refactoring.

include/wx/osx/cocoa/private.h

@@ -241,6 +241,10 @@ protected:
     // was the wx event for the current native key down event sent
     bool WasKeyDownSent() const;
 
+
+    // Return the view to apply the font/colour to.
+    NSView* GetViewWithText() const;
+
     NSEvent* m_lastKeyDownEvent;
     bool m_lastKeyDownWXSent;
 #if !wxOSX_USE_NATIVE_FLIPPED