Discover whether zmk_keymap_layer_activate is patched

`zmk_keymap_layer_activate` expects two arguments when patched with:
zmkfirmware@2a64e8a

Adding a preprocessor macro allows *modules* to detect whether the patch is
applied, so that one can invoke the function with the correct number of
arguments.

app/include/zmk/keymap.h

@@ -20,6 +20,7 @@ bool zmk_keymap_layer_active(uint8_t layer);
 bool zmk_keymap_layer_momentary(uint8_t layer);
 bool zmk_keymap_layers_any_momentary(zmk_keymap_layers_state_t layers_mask);
 uint8_t zmk_keymap_highest_layer_active(void);
+#define ZMK_TRACK_MOMENTARY_LAYER_PATCH
 int zmk_keymap_layer_activate(uint8_t layer, bool momentary);
 int zmk_keymap_layer_deactivate(uint8_t layer);
 int zmk_keymap_layer_toggle(uint8_t layer);