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GH-36399: [Python] Add missing `shape` property to `RecordBatch` (#40643)



### Rationale for this change

This property is currently missing.

### What changes are included in this PR?

Move the `shape` property to the `_Tabular` base class.

### Are these changes tested?

Yes. I've merged the `test_table_basics` and `test_record_batch` basics tests to make sure that all the same basics are tests on both classes.

### Are there any user-facing changes?

* GitHub Issue: #36399

Lead-authored-by: Judah Rand <17158624+judahrand@users.noreply.github.com>
Co-authored-by: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Signed-off-by: Joris Van den Bossche <jorisvandenbossche@gmail.com>