* [2.x] feat: Add cacheVersion setting for global cache invalidation
**Problem**
There was no escape hatch to invalidate all task caches when needed.
**Solution**
Add `Global / cacheVersion` setting that incorporates into the cache key
hash. Changing it invalidates all caches. Defaults to reading system
property `sbt.cacheversion`, or else 0L. When 0L, the hash is identical
to the previous behavior (backward compatible).
Fixes#8992
* [2.x] refactor: Simplify BuildWideCacheConfiguration and add cacheVersion test
- Replace auxiliary constructors with default parameter values
- Add unit test verifying cacheVersion invalidates the cache
* [2.x] fix: Restore auxiliary constructors for binary compatibility
* [2.x] test: Improve cacheVersion scripted test and add release note
- Scripted test now verifies cache invalidation via a counter
that increments only when the task body actually executes
- Add release note documenting the cacheVersion setting
Dream