Add support for tuple as input type to delegate in emitter. (#511)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/511

There could be instances where the input to a delegate is a tuple in itself, this is no different from supporting a list type. Adding support for this in the emitter. Export also does this where it converts a tuple input to a op to a list input.

Reviewed By: cccclai

Differential Revision: D49712806

fbshipit-source-id: 27124759f1ceaf83aefbd56a0845845390f4a0ba