Tile perf: offload tile viewmodel and data to bg

Also avoid ShareIn and use StateIn instead for the data flow

Bug: 378661321
Flag: com.android.systemui.qs_new_tiles
Test: manual. record perfetto trace, verify QSTilewViewModel.<init>
calls are not happening for spans of 10+ ms.

Change-Id: Ib163a468473be283a891dda78d232ca1ae64b336