fix: Default animatedNextPositionIndex to INITIAL_VALUE

[dfalling]

Motivation

This fix is very similar to #1035 and #1043

BottomSheet will sometimes not animate/expand because of this logic. This can happen when you have a single snapPoint, or if you use enableDynamicSizing.

Issue

animatedNextPositionIndex starts at 0, which is the same as snapPoints.length -1, causing the animation to be aborted.

Starting values:

react-native-bottom-sheet/src/components/bottomSheet/BottomSheet.tsx

Lines 239 to 240 in b6e405b

	const animatedNextPosition = useSharedValue(INITIAL_VALUE);
	const animatedNextPositionIndex = useSharedValue(0);

After a successful animation, it is reset correctly to the right value:

Reset values:

react-native-bottom-sheet/src/components/bottomSheet/BottomSheet.tsx

Lines 647 to 648 in b6e405b

	animatedNextPosition.value = INITIAL_VALUE;
	animatedNextPositionIndex.value = INITIAL_VALUE;

It should always start at INITIAL_VALUE (-Infinity) like animatedNextPosition.

Reproducing

Note: this isn't always reproducible for me. I have two identical BottomSheets, and only one of them is broken. Something in the working one is resetting the animatedNextPositionIndex.value to -Infinity before the animation runs, but I'm struggling to debug where that's happening.

[gorhom]

thanks @dfalling for submitting this PR