`Window :: #jni_class("...") { #extends View; ... }` should parse,
today's 2.3 parser doesn't recognise `#extends` as a token and the
body loop reports "expected method name". The make-green follow-up
adds `hash_extends`/`hash_implements` lexer tokens, refactors
`JniClassDecl.methods` into a `members` tagged union, and dispatches
in the body loop on the leading token.
