Fix `at::native::view_as_real()` for ComplexHalf Tensors (#43279)
Summary:
Add ComplexHalf case to toValueType, which fixes the logic how view_as_real and view_as_complex slices complex tensor to the floating point one, as it is used to generate tensor of random complex values, see:
https://github.com/pytorch/pytorch/blob/018b4d7abb894c3de21f9f10b0678c80a7b0a701/aten/src/ATen/native/DistributionTemplates.h#L200
Also add ability to convert python complex object to `c10::complex<at::Half>`
Add `torch.half` and `torch.complex32` to the list of `test_randn` dtypes
Fixes https://github.com/pytorch/pytorch/issues/43143
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43279
Reviewed By: mrshenli
Differential Revision: D23230296
Pulled By: malfet
fbshipit-source-id: b4bb66c4c81dd867e72ab7c4563d73f6a4d80a44
