ShadeControllerSceneImpl post should use main

The `post` methods in ShadeControllerScneImpl should (as their name
says) post to the main thread to interact with the shade.

Test: manual, using tile service that launches activity, targetSdk 33
Fixes: 415179281
Flag: com.android.systemui.scene_container

Change-Id: I0ad86605ddc950cd441e49cb8eec788c5e356c03