`Point :: #jni_class("...") { x: s32; y: s32; }` should parse,
today's 2.4 body loop sees the identifier `x`, expects `::`, hits
`:` and errors. The make-green follow-up adds a `field` variant to
`JniClassMember` and a parser branch that detects `<ident>:` (vs
`<ident>::`) as the field-decl indicator.
