Update LabelsJson class to not rely on Submit Rules.

Submit Rules is the old prolog-based way to define submit requirements,
it has long been deprecated. It's however still possible that some
deployments use it. So in this change we separate the old logic into
LabelsJsonRules and delegate evaluation to it, if prolog rules are in
use. This makes it easy to remove it completely in the future, once we
no longer want to support it.

In the submit rules logic, the labels are provided by defined rules.
In the case where prolog rules were disabled all the labels were being
provided by DefaultSubmitRule. In this change we adapt the logic from
DefaultSubmitRule to construct labelInfo directly.

LabelFunction has also been deprecated, but it's unclear how to get rid
of it easily. Since the `approved`, `rejected` fields are being
populated by it and has usages in Gerrit UI. SetLabelScores function
seem to fulfil similar function, but we leave that to be
refactored later. It's quite likely that further simplification to
LabelsJson are possible, but the file is hard to understand.

We are also removing LabelWithStatus class, previously labelsFor method
would drop statuses before returning anyway.

Bug: Google b/445644919
Release-Notes: skip
Forward-Compatible: checked
Change-Id: I37a8db9f0b5ffa3704523e6fb60f71197dc74fa0