CC Mode: Make c-forward-declarator move over a suffix after parens, e.g. const

CC Mode: Make c-forward-declarator move over a suffix after parens, e.g. const

Also tidy up several inaccuracies in the code.

* lisp/progmodes/cc-engine.el (c-forward-decl-arglist): Move point for modes
other than C++ Mode.
(c-forward-declarator): Move over a suffix following arglist parens
(e.g. const).  Set the ARGLIST element of the return value to non-nil on
encountering an unbalanced open parenthesis.  Don't move forward out of
enclosing parens.

* lisp/progmodes/cc-mode.el (c-fl-decl-end): Handle being in a multi-line
string.  Move forward over token after declarator.