patch 8.2.3996: Vim9: type checking lacks information about declared type

Problem:    Vim9: type checking for list and dict lacks information about
            declared type.
Solution:   Add dv_decl_type and lv_decl_type.  Refactor the type stack to
            store two types in each entry.

src/evalbuffer.c

@@ -807,12 +807,6 @@ f_getbufline(typval_T *argvars, typval_T *rettv)
     get_buffer_lines(buf, lnum, end, TRUE, rettv);
 }
 
-    type_T *
-ret_f_getline(int argcount, type_T **argtypes UNUSED)
-{
-    return argcount == 1 ? &t_string : &t_list_string;
-}
-
 /*
  * "getline(lnum, [end])" function
  */