Rewrite PIP state in Typescript (#27645)

Co-authored-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/mastodon/selectors/index.js

@@ -60,7 +60,7 @@ export const makeGetStatus = () => {
 
 export const makeGetPictureInPicture = () => {
   return createSelector([
-    (state, { id }) => state.get('picture_in_picture').statusId === id,
+    (state, { id }) => state.picture_in_picture.statusId === id,
     (state) => state.getIn(['meta', 'layout']) !== 'mobile',
   ], (inUse, available) => ImmutableMap({
     inUse: inUse && available,