Move over optional arguments in parentheses correctly

Move over optional arguments in parentheses correctly

* lisp/textmodes/reftex-parse.el (reftex-move-to-previous-arg):
Recognize ')' as closing delimiter for optional argument.
Fix docstring.
(reftex-what-macro): Identify LaTeX macros with optional arguments
in parentheses correctly.  This is necessary to make
`reftex-view-crossref' work with biblatex on entries like:
\parencites(Glob.Pre)(Glob.Post)[Pre][Post]{key1}[Pre][Post]{key2}
(bug#31132)

(cherry picked from commit 7236010d2e1d3525943bb50598d29061a4c25b58)