reuse PreG class in G class where possible

This applies the PreG change we did for gen_heap in !585 (merged) to all PreG classes, if possible. However, it turns out that this is not always possible, since some of these use a "mixin" style:

Class ownPG (Λ : language) (Σ : gFunctors) := OwnPG {
  ownP_invG : invG Σ;
  ownP_inG :> inG Σ (excl_authR (stateO Λ));
  ownP_name : gname;
}.

Class ownPPreG (Λ : language) (Σ : gFunctors) : Set := IrisPreG {
  ownPPre_invG :> invPreG Σ;
  ownPPre_state_inG :> inG Σ (excl_authR (stateO Λ))
}.

Here, we cannot make ownPPreG a field of ownPG.