[Attributor] Fold "TrackDependence" into the DepClassTy enum

We don't need a bool and an enum to express the three options we
currently have. This makes the interface nicer and much easier to
use optional dependencies. Also avoids mistakes where the bool is
false and enum ignored.

GitOrigin-RevId: e592dad82e658d635d5e957aa149f475c429e176
27 files changed