[Python] Add missing APIs to Table class

[danepitkin]

Describe the enhancement requested

The following APIs exist in the RecordBatch class, but not in the Table class:

_export_to_c _import_from_c from_struct_array to_struct_array serialize

Are any of these omitted on purpose?

Component(s)

Python

[jorisvandenbossche]

Those might be intentional differences:

• _export_to_c / _import_from_c: for RecordBatch, this exports the batch as a ArrowArray. However, that's not possible for Table, which can be chunked. In principle we could add ArrowArrayStream import/export to Table, but the Table's columns are also not guaranteed to be consistently chunked, so this might give some complexitities. Although we already support converting the Table to a RecordBatchReader (which then supports the ArrowArrayStream), and that is essentially the same conversion.
• from_struct_array / to_struct_array are specific for RecordBatch, as StructArray and RecordBatch are memory-wise almost equivalent, which is not necessarily true for a Table
• serialize writes RecordBatch to Buffer as encapsulated IPC message, but at the IPC spec level, we only have RecordBatch, and the concept of Table doesn't exist (so there is no "table" message)