parser BUGFIX text as the parent of its extension instances

The parent of the extension instances of description, reference,
prefix, presence and units is the text itself, as documented in
enum ly_stmt. The YANG parser passed the text before it was parsed,
so the parent was always NULL, and the YIN parser set NULL or, for
description and reference, the parent statement.

Both parsers now set the parsed text. It does not move with the
arrays of the parent statements, so the YIN parser no longer updates
the description and reference parents on their reallocation.

Author: Mar