add toggle focus between floating and tiled layers

Adds focus_floats(), toggle_focus_float_tiled(), and their IPC
bindings so users can bind a key to swap focus between the floating
and tiled layers.

jay-config/src/_private/ipc.rs

@@ -747,6 +747,12 @@ pub enum ClientMessage<'a> {
     SeatFocusTiles {
         seat: Seat,
     },
+    SeatFocusFloats {
+        seat: Seat,
+    },
+    SeatToggleFocusFloatTiled {
+        seat: Seat,
+    },
     SetMiddleClickPasteEnabled {
         enabled: bool,
     },