ffi 2.7 xfail: other six type-introducer directive forms parse

#jni_interface, #objc_class, #objc_protocol, #swift_class,
#swift_struct, #swift_protocol — each with the same body grammar as
#jni_class. Today the lexer doesn't recognise any of these directives
and the parser errors at the first one (`#jni_interface`). The
make-green follow-up adds the six lexer tokens and refactors
`JniClassDecl` into `ForeignClassDecl` with a `runtime` discriminator
so all seven forms share one AST shape and one parser path.

tests/expected/ffi-jni-class-07-all-runtimes.exit

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

tests/expected/ffi-jni-class-07-all-runtimes.txt

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+/Users/agra/projects/sx/examples/ffi-jni-class-07-all-runtimes.sx:20:9: error: unexpected token in expression