Add entity .trigger() methods (#14752)

# Objective

Fix https://github.com/bevyengine/bevy/issues/14233.

## Solution

Add `EntityCommands::trigger` and `EntityWorldMut::trigger`.

## Testing

- Not tested.

crates/bevy_ecs/src/system/commands/mod.rs

@@ -777,7 +777,7 @@ impl<'w, 's> Commands<'w, 's> {
         self.add(TriggerEvent { event, targets });
     }
 
-    /// Spawn an [`Observer`] and returns the [`EntityCommands`] associated with the entity that stores the observer.  
+    /// Spawns an [`Observer`] and returns the [`EntityCommands`] associated with the entity that stores the observer.
     pub fn observe<E: Event, B: Bundle, M>(
         &mut self,
         observer: impl IntoObserverSystem<E, B, M>,
@@ -1210,6 +1210,15 @@ impl EntityCommands<'_> {
         self.commands.reborrow()
     }
 
+    /// Sends a [`Trigger`] targeting this entity. This will run any [`Observer`] of the `event` that
+    /// watches this entity.
+    ///
+    /// [`Trigger`]: crate::observer::Trigger
+    pub fn trigger(&mut self, event: impl Event) -> &mut Self {
+        self.commands.trigger_targets(event, self.entity);
+        self
+    }
+
     /// Creates an [`Observer`] listening for a trigger of type `T` that targets this entity.
     pub fn observe<E: Event, B: Bundle, M>(
         &mut self,

crates/bevy_ecs/src/world/entity_ref.rs

@@ -1443,6 +1443,12 @@ impl<'w> EntityWorldMut<'w> {
         }
     }
 
+    /// Triggers the given `event` for this entity, which will run any observers watching for it.
+    pub fn trigger(&mut self, event: impl Event) -> &mut Self {
+        self.world.trigger_targets(event, self.entity);
+        self
+    }
+
     /// Creates an [`Observer`] listening for events of type `E` targeting this entity.
     /// In order to trigger the callback the entity must also match the query when the event is fired.
     pub fn observe<E: Event, B: Bundle, M>(