[MCPE-48921] [Scripting Docs] some examples need to be updated

the broadcastEvent(EventIdentifier, EventData) 's 2nd argument only accept object in 1.12, but all related examples are not been updated for this change.. (Just search `broadcastEvent` in the document)

for example:

this.broadcastEvent("minecraft:display_chat_event", "Pick at x:" + eventData.position.x + " y:" + eventData.position.y + " z:" + eventData.position.z);

need to be rewrited to

const event = this.createEventData("minecraft:display_chat_event");
event.data.message =  "Pick at x:" + eventData.position.x + " y:" + eventData.position.y + " z:" + eventData.position.z;
this.broadcastEvent("minecraft:display_chat_event", event);