Improve TS typing around view states

[kylebarron]

lonboard/src/index.tsx

Lines 103 to 104 in 6677d34

	const [initialViewState, setViewState] =
	useViewStateDebounced<MapViewState>("view_state");

lonboard/src/index.tsx

Lines 199 to 204 in 6677d34

	// This condition is necessary to confirm that the viewState is
	// of type MapViewState.
	if ("latitude" in viewState) {
	// TODO: ensure all view state types get updated on the JS side
	setViewState(viewState);
	}