Save JS method parameter counts for use at runtime
Fix creation of MatchResults from blocks in JS

Previously, these were constructed with an empty JavaScript array as
their bindings value rather than a GraceList, causing problems later on.
Launch JS debugger on getting a non-Grace receiver
Remove private fields and default to confidential
Remove "private" field error infrastructure
Clean up treatment of visibility default

Previously, a combination of special cases handled the default
visibility of fields and the overriding pragmas. Now, everything is
assumed to be confidential unless annotated otherwise. The pragmas
create the necessary annotations; no other annotation are created.