Feature: input processor behavior invocation (#2714)

refactor(pointing): Allow stopping event propagation

    Allow input processors to return a special value if a given input event
    should not be further processed/propagated.

feat(pointing): Add behavior input processor

    Add the ability to intercept certain input events and trigger behaviors
    when they occur.

Co-authored-by: Jorge Villalobos <minusfive@users.noreply.github.com>
Co-authored-by: Cem Aksoylar <caksoylar@users.noreply.github.com>

app/include/drivers/input_processor.h

@@ -13,6 +13,9 @@
 #include <zephyr/device.h>
 #include <zephyr/input/input.h>
 
+#define ZMK_INPUT_PROC_CONTINUE 0
+#define ZMK_INPUT_PROC_STOP 1
+
 struct zmk_input_processor_entry {
     const struct device *dev;
     uint32_t param1;
@@ -33,6 +36,7 @@ struct zmk_input_processor_entry {
     }
 
 struct zmk_input_processor_state {
+    uint8_t input_device_index;
     int16_t *remainder;
 };