A Component's DataType should embed its metadata

[teh-cmc]

Currently we need to carry around components' metadata (e.g. ComponentName) everywhere, because the DataType in erased arrow arrays doesn't give us any information about the component type.

This is a real issue as it prevents using DataCell in more places (too much overhead if every cell carries a ComponentName).

The solution for this is arrow2's Extension datatype; but we need to improve on the ArrowField derive macro first, so that we can specify extension metadata easily... otherwise we'd have to manually implement ArrowField for everything.

[teh-cmc]

Also: we have effectively no way of knowing whether a datatype corresponds to a cell or a whole column (or even a whole table?) just by looking at it (a component could be a list of list of list in and of itself), which is annoying.

[teh-cmc]

Related:

• Clean up Arrow extension hell, implement RERUN:component_name #3360