the original intent was to avoid having an automatic 'clone' action appearing in
the UI because some type was adaptable to IClonable. While this is still
desirable, keeping some generic UI tweaks useful to those activating the action
will be better then dropping everything at once.

Being adaptable to IClonable doesn't mean we want a clone action in the UI,
furthermore when it leads by default to the clumsy 'copy' form.

This is information that will need most custom adapters, without doing some more
heavyweight refactorings.

For instance, following non-composite relations.

Closes #15770380.

Otherwise we sometimes get cache issue, in particular with assertCountEqual
strange comparison algorithm.

The latter do not work with CubicWeb 3.23.

So that it can be used in modules not automatically reloaded without problems.

Closes #6304702.

This can be an alternative to the 'clone' action, in particular when the
'edition' form of the entity to be cloned is not readily usable (e.g. needs
tweaking to hide inlined sub-forms, etc.).

This is not ready for inclusion and was backported from client
application to soon.

This method returns a dictionary mapping entity type to composite relation
information allowing to walk the schema graph upstream from these entity
types.

* `parent_relations`/`child_relations` are used to get relation information
  from an entity type.
* `parent_structure`/`child_structure` return the full structure of the
  composite graph, this structure will change later on to conform to the
  "definition" methods.
* `parent_related`/`child_related` yield information about related entities in
  the composite graph either from the parent or child perspective.

These are used to build the IContainer/IContained classes.

This makes selections of CloneEntityHook simpler, cheaper and more robust.
Drop IClonableAdapter.clone property, not longer useful.

Also add the `structure` method which returns the fully evaluated
graph (of schema objects), useful for testing.

Actual tests are not so specific to "entities" despite most of the code
currently lies there and they are not so unit either.