WIP: Reproduce ordering errors
The ordering interface changed in !555 (merged) and some subtle problems surfaced later (See #185).
In this MR I (tried to) implement
- an empty local finite element, that can be used to manage parts of a domain that are not active
- a variable finite element map, that dynamically changes the finite element implementation per element
The test now triggers the same issue that I mentioned in #185.
- I use a dG basis that is present in some cells (fixed order) and simply empty on other cells
- The resulting space can (in principal) be blocked by cells
- the old approach would have been to use
ordering::Chunked
, which does not work anymore, as the resulting sized reported from "below" don't match anymore - the
EntityBlockedOrderingTag
doesn't work either, as it simply assumes that every cell has the same size (which we never promised, actually we report non-fixed sizes in the finite element map)