Add ability to get callback when a config entry state changes (#138943)

* Add entry_on_state_change_helper

* undo black

* remove unload

* no coro

* Add tests

* Don't accept coro

* Review feedback

* Add error test

* Make it callback type

* Make it callback type

* Removal test

* change type

homeassistant/config_entries.py

@@ -402,6 +402,7 @@ class ConfigEntry[_DataT = Any]:
     update_listeners: list[UpdateListenerType]
     _async_cancel_retry_setup: Callable[[], Any] | None
     _on_unload: list[Callable[[], Coroutine[Any, Any, None] | None]] | None
+    _on_state_change: list[CALLBACK_TYPE] | None
     setup_lock: asyncio.Lock
     _reauth_lock: asyncio.Lock
     _tasks: set[asyncio.Future[Any]]
@@ -526,6 +527,9 @@ class ConfigEntry[_DataT = Any]:
         # Hold list for actions to call on unload.
         _setter(self, "_on_unload", None)
 
+        # Hold list for actions to call on state change.
+        _setter(self, "_on_state_change", None)
+
         # Reload lock to prevent conflicting reloads
         _setter(self, "setup_lock", asyncio.Lock())
         # Reauth lock to prevent concurrent reauth flows
@@ -1058,6 +1062,8 @@ class ConfigEntry[_DataT = Any]:
             hass, SIGNAL_CONFIG_ENTRY_CHANGED, ConfigEntryChange.UPDATED, self
         )
 
+        self._async_process_on_state_change()
+
     async def async_migrate(self, hass: HomeAssistant) -> bool:
         """Migrate an entry.
 
@@ -1172,6 +1178,28 @@ class ConfigEntry[_DataT = Any]:
                 task,
             )
 
+    @callback
+    def async_on_state_change(self, func: CALLBACK_TYPE) -> CALLBACK_TYPE:
+        """Add a function to call when a config entry changes its state."""
+        if self._on_state_change is None:
+            self._on_state_change = []
+        self._on_state_change.append(func)
+        return lambda: cast(list, self._on_state_change).remove(func)
+
+    def _async_process_on_state_change(self) -> None:
+        """Process the on_state_change callbacks and wait for pending tasks."""
+        if self._on_state_change is None:
+            return
+        for func in self._on_state_change:
+            try:
+                func()
+            except Exception:
+                _LOGGER.exception(
+                    "Error calling on_state_change callback for %s (%s)",
+                    self.title,
+                    self.domain,
+                )
+
     @callback
     def async_start_reauth(
         self,