vim-patch:8.2.0512: Vim9: no optional arguments in func type

Problem:    Vim9: no optional arguments in func type.
Solution:   Check for question mark after type.  Find function reference
            without function().

5deeb3f1f9

Co-authored-by: Bram Moolenaar <Bram@vim.org>

src/nvim/eval/typval_defs.h

@@ -326,7 +326,7 @@ struct ufunc {
   int uf_flags;
   int uf_calls;         ///< nr of active calls
   bool uf_cleared;       ///< func_clear() was already called
-  garray_T uf_args;          ///< arguments
+  garray_T uf_args;          ///< arguments, including optional arguments
   garray_T uf_def_args;      ///< default argument expressions
   garray_T uf_lines;         ///< function lines
   int uf_profiling;     ///< true when func is being profiled