Introduce CA_TOPLEVEL to collect_args to replace parse_method_decl
Introduce CA_TOPLEVEL to collect_args to replace parse_method_decl

collect_args and parse_method_decl were doing a lot of the same work except
that collect_args didn't have a way to capture named arguments within a named
method. CA_TOPLEVEL will cause collect_args to do so. Removed
parse_method_decl, since it's now obsolete.

The simple version: A lot of redundant code was removed.

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