gsturi: Add new API for storing unmodified userinfo / fragment
New API: gst_uri_from_string_escaped()
Identical to gst_uri_from_string()
except that the userinfo and
fragment components of the URI will not be unescaped while parsing.
This is needed for correctly parsing usernames or passwords with :
in them such as reported at: gst-plugins-bad#831 (closed)