Allow entries as args in custom statements (#498)

- Introduce a new operation ReplaceValueWithEntry that allows taking any statement and replacing literal arguments with entries given a matching Contains statement.
- Allow entries as args in custom statements
- Circuit optimization: For the public statements slots in the circuit we only support None and Copy which take at most 1 argument; but we were still doing max_statement_args random accesses per slot; so I reduced that to just 1 random access to a previous statement.

src/lang/diagnostics.rs

@@ -174,18 +174,6 @@ fn render_validation_error(
             "second REQUEST here",
         ),
 
-        ValidationError::InvalidArgumentType { predicate, span } => {
-            let title = format!("invalid argument type for `{}`", predicate);
-            render_with_optional_span(
-                renderer,
-                source,
-                path,
-                &title,
-                span.as_ref(),
-                "anchored keys not allowed here",
-            )
-        }
-
         ValidationError::DuplicateWildcard { name, span } => {
             let title = format!("duplicate wildcard: {}", name);
             render_with_optional_span(