Changelog for face -> facet changes

[fredrikekre]

#914 is missing changelog entries for user-facing changes:

• getfaceset -> getfacetset, addfaceset! -> addfacetset!
• addboundaryfaceset! -> addboundaryfacetset!
• getedgeset, addedgeset!, addboundaryedgeset
  No direct replacement, but Ferrite.create_edgeset and Ferrite.create_boundaryedgeset gives equivalent functionality (for 3d cases) for sets not stored in the grid.
• FaceValues -> FacetValues
• AbstractFacetValues -> AbstractFacetValues (why is this exported?)
• Ferrite.getcurrentface -> Ferrite.getcurrentfacet
• FaceQuadratureRule -> FacetQuadratureRule
• nfaces -> nfacets
• FaceIterator -> FacetIterator
• FaceCache -> FacetCache
• collect_periodic_faces -> collect_periodic_facets
• PeriodicFacePair -> PeriodicFacetPair (why is this exported?)

Anything else?

[KnutAM]

(Edited the list above)

Technically Ferrite.n_faces_per_cell -> Ferrite.n_facets_per_cell as well, but this is not used/tested and seems to only be overloaded for the SmallGrid. Will open PR to remvoe this completely.

[termi-official]

Yea, I would also vote for removing such "global" queries on the grid, since they cause more harm than good. Or we rename then to "max_faces_per_cell" or smth, which could be used to create buffers which are "large enough".

[KnutAM]

Removed in #921

[KnutAM]

Closed in #940