Prevent constant recomposition of TileGrid

Using flow operators in a Composable will cause constant recompositions,
instead collect to a State and transform that.

Also, make some key classes @Immutable

Test: manual, log recompositions
Bug: 331598956
Flag: com.android.systemui.qs_ui_refactor
Change-Id: I92e371db9ae7e0270c2e0b3043cb18a27839b80c