Added linalg.pinv (#48399)
Summary:
This PR adds `torch.linalg.pinv`.
Changes compared to the original `torch.pinverse`:
* New kwarg "hermitian": with `hermitian=True` eigendecomposition is used instead of singular value decomposition.
* `rcond` argument can now be a `Tensor` of appropriate shape to apply matrix-wise clipping of singular values.
* Added `out=` variant (allocates temporary and makes a copy for now)
Ref. https://github.com/pytorch/pytorch/issues/42666
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48399
Reviewed By: zhangguanheng66
Differential Revision: D25869572
Pulled By: mruberry
fbshipit-source-id: 0f330a91d24ba4e4375f648a448b27594e00dead
