Add more lemmas for FinMaps (for union, filter, difference)

See merge request iris/stdpp!245

Generalize `map_filter_insert` so that it covers both the True and False case.

See merge request iris/stdpp!310

Use `_True` and `_False` for the specific cases.

Weaken premise of `map_filter_delete_not` and make it consistent with `map_filter_insert_not'`.

Clean up `empty{',_inv,_iff}` lemmas.

See merge request iris/stdpp!307

Write them all using `` and consistently use the `_iff` suffix.

some lemmas about list submseteq

See merge request iris/stdpp!305

Add lemma `map_singleton_subseteq_l` and `map_singleton_subseteq`.

See merge request iris/stdpp!308

Make singleton/`⊆` lemmas consistent with Iris's singleton/`≼`

See merge request iris/stdpp!306

Rename `gmultiset_elem_of_singleton_subseteq` → `gmultiset_singleton_subseteq_l` and swap order to be consistent with Iris's `singleton_included_l`.

Add lemmas that say that `curry{3,4}?` and `uncurry{3,4}?` are inverses.

See merge request iris/stdpp!304

solve_ndisj: handle goals containing _ ∖ _ ∖ _

See merge request iris/stdpp!303

`Params` and `Proper` instances for `curry` and friends

See merge request iris/stdpp!302