Using `objectid` as a dict key is wrong

[Technici4n]

Two different objects may have the same objectid. Things like

    id_pair = (objectid(x), objectid(y))
    haskey(d, id_pair) && return d[id_pair]

as done in TestUtils.has_equal_data_internal thus have a small chance to be wrong.

It would be preferable to use an IdDict with (x, y) as the key, I believe.