Don't install a pointer input when a NestedDraggable is disabled

This CL is inspired from ag/29699552: when a Modifier.nestedDraggable is
disabled, we make sure that we don't even install a
PointerInputModifierNode so that gestures will be dispatched to siblings
with lower z-Indices.

Bug: 378470603
Test: atest NestedDraggableTest
Flag: EXEMPT NestedDraggable is not used yet
Change-Id: Id596d79f733cd7d1c633a6f456809e7a30b74945