internal/core/adt: do not activate ids for non-definitions

Observe forceIgnore when we decide to activate
a requirement.

This possibly opens up the conjuncts from API calls.
To ensure closedness from such calls is always
preserved, we have a separate flag (TopDef) that
gets cleared and changed into a FromDef after
the first application.

Fixes #3585

Signed-off-by: Marcel van Lohuizen <[email protected]>
Change-Id: I59c241a8eb980b41f0d092c8bbfeb15da7076e67
Reviewed-on: https://cue.gerrithub.io/c/cue-lang/cue/+/1212514
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Daniel Martí <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

Author: mpvl