feat(bluetooth): Proper bond management, identity support for non-splits

* Add `bt` behavior that can be used to perform certain actions,
  such as next/prev identity, reset identity, etc.
  NOTE: Multiple identities is only supported for non-split shields,
  due to missing Zephyr identity functionality for dual
  central/peripheral devices.
* Proper bond reset tied to action, that honors peripheral bonds,
  so folks can reset and pair to other hosts, without breaking
  bonds between splt halves.

app/dts/behaviors.dtsi

@@ -7,4 +7,5 @@
 #include <behaviors/toggle_layer.dtsi>
 #include <behaviors/reset.dtsi>
 #include <behaviors/sensor_rotate_key_press.dtsi>
-#include <behaviors/rgb_underglow.dtsi>
+#include <behaviors/rgb_underglow.dtsi>
+#include <behaviors/bluetooth.dtsi>

app/dts/behaviors/bluetooth.dtsi

@@ -0,0 +1,9 @@
+/ {
+	behaviors {
+		bt: behavior_bluetooth {
+			compatible = "zmk,behavior-bluetooth";
+			label = "BLUETOOTH";
+			#binding-cells = <2>;
+		};
+	};
+};

app/dts/bindings/behaviors/zmk,behavior-bluetooth.yaml

@@ -0,0 +1,8 @@
+# Copyright (c) 2020, Peter Johanson
+# SPDX-License-Identifier: MIT
+
+description: Bluetooth Behavior
+
+compatible: "zmk,behavior-bluetooth"
+
+include: two_param.yaml