Yang 1.0: Shorthand case should create case node in schema tree

Yang 1.1 requires this explicitly. https://tools.ietf.org/html/draft-ietf-netmod-rfc6020bis-14#section-7.9.2

Yang 1.0 mentions case nodes for omitted case statements, but does not explicitly require case nodes to be present in schema tree. https://tools.ietf.org/html/rfc6020#section-7.9.2

Current parser implementation seems so omit case nodes also in schema tree, which may lead to users creating Yang 1.1 incompatible modules.
This Change Request is opened so that this particular behavioral change is separated from real incompatibilities between 1.0 and 1.1 semantics.

Example model to follow shortly.