Implement From<&'w mut EntityMut> for EntityMut<'w> (#12896)

# Objective

- Implement `From<&'w mut EntityMut>` for `EntityMut<'w>`;
- Make it possible to pass `&mut EntityMut` where `impl Into<EntityMut>`
is required;
- Helps with #12895.

## Solution

- Implement `From<&'w mut EntityMut>` for `EntityMut<'w>`

---

## Changelog

- `EntityMut<'w>` now implements `From<&'w mut EntityMut>`

crates/bevy_ecs/src/world/entity_ref.rs

@@ -469,6 +469,12 @@ impl<'w> EntityMut<'w> {
     }
 }
 
+impl<'w> From<&'w mut EntityMut<'_>> for EntityMut<'w> {
+    fn from(value: &'w mut EntityMut<'_>) -> Self {
+        value.reborrow()
+    }
+}
+
 impl<'w> From<EntityWorldMut<'w>> for EntityMut<'w> {
     fn from(value: EntityWorldMut<'w>) -> Self {
         // SAFETY: `EntityWorldMut` guarantees exclusive access to the entire world.