Testing: split ble encoder test (#2754)

test(sensors): Add mock encoder sensor

Add a new mock sensor driver for generating mock encoder sensor channel
data.

test(split): Add a peripheral sensor split test

Test BLE split logic for peripheral sensors (encoders).

app/tests/ble/split/peripheral-encoder/nrf52_bsim.keymap

@@ -0,0 +1,23 @@
+#include <behaviors.dtsi>
+#include <dt-bindings/zmk/bt.h>
+#include <dt-bindings/zmk/keys.h>
+
+#include "shared.dtsi"
+
+&kscan {
+    /delete-property/ exit-after;
+    events = <>;
+};
+/ {
+    keymap {
+        compatible = "zmk,keymap";
+
+        default_layer {
+            bindings = <
+            &kp A &kp B
+            &bt BT_SEL 0 &bt BT_CLR>;
+
+            sensor-bindings = <&inc_dec_kp A B>;
+        };
+    };
+};