Currently, tables inside a slide are considered as an `Unsupported` type and cannot get any textFrame (or other properties/methods) from the table rows (as far as I read and tried).
I think tables are frequently used in slides, and so providing an API for interacting with a them will come in handy. Especially for an add-in to help out with grammar/spelling, by not being able to interact with a table, it leaves a big hole.
Please let me know if I should add additional information.