testing: Add split BLE tests (#2737)

* Enhance the BLE test runner to build additional peripheral builds
  when detecting peripheral*.overlay files in the test.
* Add basic and multiple-peripheral tests to exercise the testing
  support
* Add test for triggering local behaviors on split peripherals.

fix(ble): Fix building split code w/o settings

* Properly exclude storing peripheral addresses to settings when
  settings support isn't turned on.

app/tests/ble/split/basic/nrf52_bsim.keymap

@@ -0,0 +1,19 @@
+#include <behaviors.dtsi>
+#include <dt-bindings/zmk/bt.h>
+#include <dt-bindings/zmk/keys.h>
+
+&kscan {
+    /delete-property/ exit-after;
+    events = <>;
+};
+/ {
+    keymap {
+        compatible = "zmk,keymap";
+
+        default_layer {
+            bindings = <
+            &kp A &kp B
+            &bt BT_SEL 0 &bt BT_CLR>;
+        };
+    };
+};