meta/with-meta resolved to jolt-nil. Chez values don't carry metadata, so
collections use an identity-keyed side-table: with-meta returns a fresh copy of
the value (new identity) and records its meta there, leaving the original
unchanged (immutable-with-meta) and dropping meta on a later copying op. Symbols
carry meta in their existing field; meta on a non-metadatable value is nil.
vary-meta works over these. with-meta on a fn stays fn? (jolt is lenient).
emit.janet carries a quoted symbol's reader metadata (^:foo bar) onto the
emitted jolt-symbol so (meta 'x) sees it; symbol = still ignores meta.
Prelude parity 1701 -> 1723, 0 new divergences. jolt-rkbc.
