sloppyfocus: revert to original setFocus() activation

The port regressed because I replaced the original's pane->setFocus() with
MainWindow::activateView() on a theory that setFocus() didn't move Kate's focus.
The original logic was correct and working; activateView() broke it (and can't
target the pointed pane for a split of the same document). Restore the exact
original activation. The port is now logic-identical to the standalone plugin;
confirmed working in a live split.

src/sloppyfocus/sloppyfocusplugin.h

@@ -14,6 +14,7 @@
 #define DEFT_SLOPPYFOCUSPLUGIN_H
 
 #include <KTextEditor/ConfigPage>
+#include <KTextEditor/Document>
 #include <KTextEditor/MainWindow>
 #include <KTextEditor/Plugin>
 #include <KTextEditor/View>