Don't restart the drag gesture when the matcher changes.

[m-sasha]

We currenty restart the drag gesture detector when the pointer matcher changes:

        Modifier.pointerInput(matcher) {
            detectDragGestures(
                matcher = matcher,
                onDragStart = { onDragStartState.value(it) },
                onDrag = { onDragState.value(it) },
                onDragEnd = { onDragEndState.value() },
                onDragCancel = { onDragCancelState.value() }
            )
        }

This means that, for example,

@OptIn(ExperimentalFoundationApi::class)
fun main() = singleWindowApplication {
    var n by remember { mutableStateOf(0) }
    Box(
        modifier = Modifier
            .fillMaxSize()
            .background(Color.LightGray)
            .onDrag(matcher = PointerMatcher.mouse(PointerButton.Primary)) {
                println("Dragged: $it")
                n += 1
            }
    ) {
        Text(n.toString())
    }
}

will not work.

Proposed Changes

• Make PointerMatcher a fun interface (because it's fun!!)
• Remember the updated matcher and use it instead of restarting the pointer input scope.

Testing

Test: Added a unit test.

[m-sasha]

Adding Igor because making PointerMatcher a fun interface is possibly (but unlikely, I think) a source-level breaking change. #kotlin channel confirmed it's not a binary-breaking change.

But I think it's a good change in general, and the API is still experimental, so I put it in.