builtins: accept the 4-argument (order) form of isdefinedglobal (#62447)
`jl_f_isdefinedglobal` declared `JL_NARGS(isdefined, 2, 3)`, so its
4-argument `isdefinedglobal(m, s, allow_import, order)` branch was
unreachable and a dynamic call passing an order threw "too many
arguments" -- contradicting the builtin's own documented signature and
the abstract model. Accept up to 4 arguments and read the order from
`args[3]` (it had read `args[2]`, the `allow_import` slot). With this,
`isdefinedglobal_partition` can just delegate the order through to
`isdefinedglobal` rather than re-validating it itself.
Bug introduced by #56985
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>