Move class-related flags off fragments and compute them directly on
`ClassElementImpl`. This reduces coupling to fragments and avoids
duplicated logic.
Changes:
- Compute `isConstructable` as `!isSealed && !isAbstract` instead of
delegating to `_firstFragment`.
- Compute `isExhaustive` as `isSealed`.
- Remove `hasGenerativeConstConstructor`, `isConstructable`, and
`isExhaustive` getters from `ClassFragmentImpl`.
- In constant verifier, resolve the enclosing class via
`container.declaredFragment!.element` and check `ClassElementImpl`
rather than fragment types.
Why:
- Centralizes flag computation on the element, making semantics clearer.
- Decreases fragment dependencies and maintenance surface.
Change-Id: I4b7153a4a55037e6dc12e18a32161a3472902eeb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/446008
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Konstantin Shcheglov
9eb648a124