C++ Mode: Fontify functions correctly with commas in template expressions

C++ Mode: Fontify functions correctly with commas in template expressions

This fixes bug #57318.

Also apply an optimization which marks generic expressions as already
analyzed, thus avoiding repeating this analysis when not needed.  This
optimization prevents the fix slowing down scrolling when the C++ source has
lots of template structures.

* lisp/progmodes/cc-engine.el (top-level) Near the beginning of the file, add
a comment describing the new text property c-<>-c-types-set.
(c-update-brace-stack): Bind c-restricted-<>-arglists to nil rather than t
around the call to c-forward-<>-arglist.
(c-forward-<>-arglist-recur): Allow the abbreviated analysis of a generic
expression also when the opening < is marked with a c-<>-c-types-set text
property.  Set this property at the same time as the c-type properties are set
on the commas inside the template structure.

* lisp/progmodes/cc-fonts.el (c-font-lock-complex-decl-prepare): Clear the
c-<>-c-types-set text property, along with c-type, from the region being
fontified.