[SystemUiController] Update SystemUiController to hoist dark theme

[alexvanyo]

Reworks the primary docs entrance to the system ui controller module slightly.

First, it removes the reference to MaterialTheme.colors.isLight. This is M2 specific, and doesn't exist in M3 in favor of hoisting the decision directly.

Second, it replaces SideEffect with a DisposableEffect with keys. I could go either way here, but I'm less of a fan of the implicit nature in how SideEffect reruns. It's not super obvious that this wouldn't work when useDarkIcons changes:

val systemUiController = rememberSystemUiController()
var useDarkIcons by remember { mutableStateOf(false) }

SideEffect {
    systemUiController.setSystemBarsColor(
        color = Color.Transparent,
        darkIcons = useDarkIcons
    )
}

[bentrengrove]

SideEffect runs on every recomposition, why wouldn't your above example work?

[alexvanyo]

SideEffect runs on every recomposition, why wouldn't your above example work?

That's true, but SideEffect will only recompose once.
Since var useDarkIcons is using a delegate, no state reads happen in the outer scope, so the SideEffect won't be recompose when useDarkIcons changes. Unless there are other state reads of it later.