Fix light client informant while syncing (#9932)

* Add `is_idle` to LightSync to check importing status

* Use SyncStateWrapper to make sure is_idle gets updates

* Update is_major_import to use verified queue size as well

* Add comment for `is_idle`

* Add Debug to `SyncStateWrapper`

* `fn get` -> `fn into_inner`

parity/informant.rs

@@ -184,7 +184,7 @@ impl InformantData for LightNodeInformantData {
 	fn executes_transactions(&self) -> bool { false }
 
 	fn is_major_importing(&self) -> bool {
-		self.sync.is_major_importing_no_sync()
+		self.sync.is_major_importing()
 	}
 
 	fn report(&self) -> Report {