Parser: jp-parse-postfix handles op "?." followed by ident / [ / (
emitting (js-optchain-member obj name), (js-optchain-index obj k),
or (js-optchain-call callee args).
Transpile: each emits (js-optchain-get obj key) or (js-optchain-call
fn args).
Runtime: js-optchain-get and js-optchain-call short-circuit to
js-undefined when receiver is null/undefined.
423/425 unit (+5), 148/148 slice unchanged.
giles
18ae63b0bd