Fix DM percent rendering, add checks for limits

[hasty]

This PR fixes the incorrect rendering of percent limits in the data model.

It also adds a new framework for checking constraint limits and fallbacks, and adds a couple checks:

1. That limits on percentage and percentage100ths fields should be expressed as percentages
2. That limits on percentage fields must be whole percentages
3. That limits on percentage100ths fields can not have more than two decimals
4. That null fallbacks can't exist on non-nullable fields

That last one causes a failure on the current spec: the AmbientContextDetectStarted event has a non-nullable ObjectCount field with a fallback of null. We should fix that before merging this.

[mergify]

This pull request does not currently match the merge queue conditions, so it cannot be queued from here. The box comes back if it matches again.

[AryaHassanli]

Thank you @hasty for the PR. Could you please fix the failing test?

[hasty]

Thank you @hasty for the PR. Could you please fix the failing test?

Done!