tl;dr - deterministic function that compares arbitrary objects
I know now we have `Map` and `Set`, but sometimes we need more low level
ones. Especially for library developers.
For the case, say, I want to implement a map whose key can be a arbitrary
number of objects. Currently this can only implemented as nested map whose
structure is `keylen -> key1 -> key2 -> ... -> value`. Not really elegant.
But if we have `Object.compare()`, `(key1, key2, ...) -> value` is possible.
As its intended purpose is to be used with custom map/set, I don't think we
should define how this function works in spec. Just guaranteed to be
deterministic in each runtime is enough.
For detail, this function follows `(left: any, right: any) => number` form.
When `Object.is(left, right)` is true, `Object.compare(left, right)` must
return `0`. Otherwise, the result must be deterministic, means whenever(in
same runtime) we call this function with same arguments it should return
same value(or at least, always greater than/lesser 0).
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