Move cooked_index_functions to cooked-index.h

This moves the declaration of cooked_index_functions to
cooked-index.h.  This makes it visible for use by the rewritten
.debug_names reader, and it also lets us move the implementation of
make_quick_functions into cooked-index.c, where it really belongs.

gdb/dwarf2/cooked-index.c

@@ -616,6 +616,12 @@ cooked_index::get_main () const
   return best_entry;
 }
 
+quick_symbol_functions_up
+cooked_index::make_quick_functions () const
+{
+  return quick_symbol_functions_up (new cooked_index_functions);
+}
+
 /* See cooked-index.h.  */
 
 void