Use RootNode.cloneRootNode to avoid inconsistencies in AST

Note, this API is only available in my private fork of Graal.

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Fix a bug in inliner, which returned the un-corrected root node

If the root node given to the visitor was changed, we would still return it. Instead, we need to return the child node of the dummy parent.

Signed-off-by: Stefan Marr <git@stefan-marr.de>