Convert meta::declaration to Cpp2

This one is nice -- order independence means I can stop having to define the `make_` functions out-of-line and put them back in the type body where they belong and are easier to read (and save a few more LOC)

Author: hsutter

regression-tests/test-results/version

@@ -1,5 +1,5 @@
 
-cppfront compiler v0.2.1   Build 8507:1612
+cppfront compiler v0.2.1   Build 8507:1624
 Copyright(c) Herb Sutter   All rights reserved
 
 SPDX-License-Identifier: CC-BY-NC-ND-4.0