[FFI] fix two seemingly migration issue

[wrongtest-intellif]

• Allow i64 any value convert to Integer of proper bitwidth.

  import tvm
  from tvm import relax
  x = relax.Var("x", relax.TensorStructInfo((5, 784), "float32"))
  # just build an object with `Integer` typed field.
  x = relax.op.flip(x, 2**63-1).attrs.axis
  # maybe better to get T.int64(9223372036854775807) rather than -1

• Ensure None any value's v_int64=0, since AnyHash depends on the repr value.

  m = tvm.ir.Map({None: 1})
  assert None in m   # get False if v_int64 not const initialized.