ffi 2.5 xfail: name: Type; field body item in #jni_class

`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.

tests/expected/ffi-jni-class-05-field.exit

@@ -0,0 +1 @@
+1

tests/expected/ffi-jni-class-05-field.txt

@@ -0,0 +1 @@
+/Users/agra/projects/sx/examples/ffi-jni-class-05-field.sx:12:6: error: expected '::'