Partial object rules with "key override" rules cause non-deterministic type-checking

[johanfylling]

This issue deals with the intermittent type-checker behavior discussed in #6138.

Given the following policy:

package test

obj.foo := 42

obj[k] := v {
    v := ["a", "b", "c"][k]
}

test_obj {
    obj == {
        0: "a",
        1: "b",
        2: "c",
        "foo": 42,
    }
}

compilation will fail intermittently, as rules aren't properly sorted before type-checking occurs. If a partial rule (data.test.obj) has a "child" rule (data.test.obj.foo) declaring a "key override", it is left to chance whether all rules contributing to the partial object's type have been added to the type-tree before type-checking is performed on any dependent rule (data.test.test_obj).