Commit #93b7a4 added support for pre-configuring URI variables at the
UriComponentsBuilder level, and also changed toUriString to encode
template and URI variables separately. However this went a bit too far
causing side effects for URLs with curly braces that don't represent
URI variables.
This commit restores the original toUriString behavior which is to
encode template and URI variables sepraately only if URI variables have
been pre-configured.
Issue: SPR-17630
c6e50087a0