splitFragmentInContainer function
Splits fragment at offset and inserts the right part in the container
immediately after fragment. Returns the right Fragment.
Implementation
Fragment splitFragmentInContainer(
InlineContainerNode container, Fragment fragment, int offset) {
final (:left, :right) = FragmentOperations.splitFragment(fragment, offset);
final children = container.getChildren();
final idx = children.indexWhere((c) => c.id == left.id);
if (idx >= 0) children.insert(idx + 1, right);
return right;
}