Add wxDocument::Activate() method.

Make activating the first (and, in the vast majority of cases, the only) view
of the document easier.

Closes #15120.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73720 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/docview.h

@@ -1240,6 +1240,15 @@ public:
      */
     bool AlreadySaved() const;
 
+    /**
+        Activate the first view of the document if any.
+
+        @see GetFirstView()
+
+        @since 2.9.5
+     */
+    void Activate() const;
+
     /**
         Closes the document, by calling OnSaveModified() and then (if this
         returned @true) OnCloseDocument(). This does not normally delete the