Fix MediaCarousel position in QS

There was a few issues:
1) Wrapping MediaCarousel into a Box instead of a Column broke MediaCarousel in QS;
2) My recent change to WindowSizeClass introduced unnecessary remember
   and prevented `LocalWindowSizeClass.current` from updating;

Flag: com.android.systemui.scene_container
Fixes: 367334276
Test: manual on foldable. Open shade and go to QS. Do this for portrait,
landscape and bigscreen configs.

Change-Id: I4c9beb84803380c69b434e339c9bbed636362be3