Restore unrecognized statement defensiveness

Restore unrecognized statement defensiveness

We are in a bad place here, as we are trying to come up with
something that passes for a QName based on zero understanding
of argument structure.

Previous cleanup of the logic here, done in YANGTOOLS-1191
omitted a possible source of errors -- when the value contains
something resembling a qualified node identier to the point
of actually resolving to a module -- but the localname part
is not actually valid.

Fix this by going through UnqualifiedQName.tryCreate(), just
as we do in the unqualified case.

The test model is a simplified version of tailf yang models
(specifically "tailf-ncs-devices@2020-02-04.yang" model), where
the argument structure is actually a descendant schema node
identifier.

JIRA: YANGTOOLS-1261
Change-Id: I885828221382f5689b491f26161b35987dfd4482
Signed-off-by: Samuel Kontris <samuel.kontris@pantheon.tech>
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>