* Invalidate `decl_val` dependencies
* Recursively mark and un-mark all dependencies correctly
* Queue analysis of outdated dependers in `Compilation.performAllTheWork`

Introduces logic to invalidate `decl_val` dependencies after
`Zcu.semaDecl` completes. Also, recursively un-mark dependencies as PO
where needed.

With this, all dependency invalidation logic is in place. The next step
is analyzing outdated dependencies and triggering appropriate
re-analysis.