Handle missing data types. (#2984)

Summary:
**Changes**
- The runtime was failing if it encountered a datatype not supported by CoreML framework. The changes add support for all the datatypes that are supported by coremltools basically if `CoreMLBackend` can export a model then runtime would execute it. Complex types are not supported because `coremltools` doesn't support it.

- Improves and cleans the multiarray copying code.

- Adds portable ops to CoreML executor so that it can run a partitioned model.

**Testing**
- Tested partitioned model `coreml_stories.pte`
- Added multiarray copying tests.

Pull Request resolved: https://github.com/pytorch/executorch/pull/2984

Reviewed By: kirklandsign

Differential Revision: D56003795

Pulled By: shoumikhin

fbshipit-source-id: fa1c7846f9510d68c359aed6761aedb2d10c6f46