fix(bt): declare esp_event as a private requirement

bt sources include esp_wifi_types.h via esp_blufi_api.h, which
transitively includes esp_event_base.h from the esp_event component.

components/bt/CMakeLists.txt

@@ -89,6 +89,7 @@ set(bt_priv_requires
     esp_ringbuf
     esp_gdbstub
     esp_security
+    esp_event
 )
 
 idf_component_register(SRCS "${srcs}"