For all big_op lemmas which had an `Absorbing` condition, the condition
has now become an alternative between `Affine` and `Absorbing`. Thus the
lemmas are made more general. This change is spreading the use of the
`TCOr (Affine _) (Absorbing _)` pattern.

Strengthen `big_sepL_submseteq` and `big_sep{M,S,MS}_subseteq` to only require the predicate to be affine, instead of the whole BI.

The goal is to become consistent with the new lemmas for `big_andM` in !713.

also add `wand_entails'`, which was used in some earlier version of these proofs

Thank you, Robbert.

Add lemmas `big_sepM2_delete_{l,r}` and rename `big_sepM2_lookup_{1,2}` into `big_sepM2_lookup_{l,r}`.