feat(behaviors): Add behavior metadata information.

* For upcoming ZMK studio work, make a set of rich metadata available
  to provide a friendly name for a behavior, and allow super flexible
  descriptions of the parameters the behaviors take.
* Add ability to validate a zmk_behavior_binding against
  the behavior metadata available.

app/dts/behaviors/toggle_layer.dtsi

@@ -9,6 +9,7 @@
         /omit-if-no-ref/ tog: toggle_layer {
             compatible = "zmk,behavior-toggle-layer";
             #binding-cells = <1>;
+            display-name = "Toggle Layer";
         };
     };
 };