layer-shell: Refocus the keyboard focus view after arranging layers

This effectively makes it so the view that had focus before interacting
with wf-shell apps, is focused after interactivity is complete.

Fixes #2118.
Fixes #2047.

src/view/layer-shell/layer-shell.cpp

@@ -378,6 +378,7 @@ struct wf_layer_shell_manager
         arrange_layer(output, ZWLR_LAYER_SHELL_V1_LAYER_BOTTOM);
         arrange_layer(output, ZWLR_LAYER_SHELL_V1_LAYER_BACKGROUND);
         output->workarea->reflow_reserved_areas();
+        wf::get_core().seat->refocus();
     }
 };