[pattgen/dv] Inactive level feature: scoreboard modeling and coverage measurement

PR #23198 added the *inactive level* feature to pattgen. That PR contains the new `pattgen_inactive_level_vseq` to activate that feature. As pattgen's scoreboard currently doesn't model this feature, it is presently deactivated in that vseq.

We need to:
- [ ] model this feature in the scoreboard and activate the scoreboard in `pattgen_inactive_level_vseq`
- [ ] add coverpoints to measure the feature
- [ ] if needed based on coverage results, extend `pattgen_inactive_level_vseq` to close coverage over the feature
- [ ] remove the `TODO(#23219)` comments in the code