fix(msg): make it work with Micropython (#3488)

* fix(msg): fill callback prototype

lv_msg_subscribe_cb_t does not follow the callback conventions.
Remove unused void* argument to fix that.

* fix(msg):  move subs_ll to gc roots

* fix(msg): rename subsribe to subscribe

* fix(msg): update docs

* fix(msg): Add example_1

* fix(msg): fix include paths

* fix(mgs): Fix python example typo and comments

* fix(msg):  LV_EVENT_MSG_RECEIVED event code

examples/others/msg/lv_example_msg_1.py

@@ -0,0 +1,39 @@
+
+# Define a message ID
+MSG_NEW_TEMPERATURE = const(1)
+
+# Define the object that will be sent as msg payload
+class Temperature:
+    def __init__(self, value):
+        self.value = value
+    def __repr__(self):
+        return f"{self.value} °C"
+
+def slider_event_cb(e):
+    slider = e.get_target()
+    v = slider.get_value()
+    # Notify all subscribers (only the label now) that the slider value has been changed
+    lv.msg_send(MSG_NEW_TEMPERATURE, Temperature(v))
+
+def label_event_cb(e):
+    label = e.get_target()
+    msg = e.get_msg()
+    # Respond only to MSG_NEW_TEMPERATURE message
+    if msg.get_id() == MSG_NEW_TEMPERATURE:
+        payload = msg.get_payload()
+        temprature = payload.__cast__()
+        label.set_text(str(temprature))
+
+# Create a slider in the center of the display
+slider = lv.slider(lv.scr_act())
+slider.center()
+slider.add_event_cb(slider_event_cb, lv.EVENT.VALUE_CHANGED, None)
+
+# Create a label below the slider
+label = lv.label(lv.scr_act())
+label.add_event_cb(label_event_cb, lv.EVENT.MSG_RECEIVED, None)
+label.set_text("0%")
+label.align(lv.ALIGN.CENTER, 0, 30)
+
+# Subscribe the label to a message
+lv.msg_subscribe_obj(MSG_NEW_TEMPERATURE, label, None)