c-get-fontification-context: Refine the last non-default arm of the cond

c-get-fontification-context: Refine the last non-default arm of the cond

This fixes bug #58772.

* lisp/progmodes/cc-fonts.el (c-get-fontification-context): Make the function
return (decl . nil) when MATCH-POS is in the second paren list of something
like DEFUN (..) (..).  Tidy up untidy code with save-excursion's for greater
accuracy.  Set a c-type text property value c-decl-arg-start to speed up
future calls.  Reindent the entire function.