Previously, YJIT returned truthy for the block given query at the top
level. That's incorrect because the top level script never receives a
block, and `yield` is a syntax error there.
Inside methods, the number of hops to get from `iseq` to
`iseq->body->local_iseq` is the same as the number of
`VM_ENV_PREV_EP(ep)` hops to get to an environment with
`VM_ENV_FLAG_LOCAL`. YJIT and the interpreter both rely on this as can
be seen in get_lvar_level(). However, this identity does not hold for
the top level frame because of vm_set_eval_stack(), which sets up
`TOPLEVEL_BINDING`.
Since only methods can take a block that `yield` goes to, have ISEQs
that are the child of a non-method ISEQ return falsy for the block given
query. This fixes the issue for the top level script and is an
optimization for non-method contexts such as inside `ISEQ_TYPE_CLASS`.
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