[WIP] Port MONAI Generative utils

[marksgraham]

Towards completing #6676 .

Description

A few sentences describing the changes proposed in this pull request.

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• Quick tests passed locally by running ./runtests.sh --quick --unittests --disttests.
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.

[marksgraham]

@ericspod I'm getting mypy errors from unsqueeze_left and unsqueeze_right:

mypy 1.4.1 (compiled: yes)
monai/utils/misc.py:895:5: error: Returning Any from function declared to return "T"  [no-any-return]
monai/utils/misc.py:895:12: error: Value of type "object" is not indexable  [index]
monai/utils/misc.py:895:43: error: "T" has no attribute "ndim"  [attr-defined]
monai/utils/misc.py:900:5: error: Returning Any from function declared to return "T"  [no-any-return]
monai/utils/misc.py:900:12: error: Value of type "object" is not indexable  [index]
monai/utils/misc.py:900:34: error: "T" has no attribute "ndim"  [attr-defined]

so far they only operate on tensors - am I ok to type them specifally for tensors/np arrays to satisfy mypy?

[ericspod]

am I ok to type them specifally for tensors/np arrays to satisfy mypy?

If you need to yes do that, but we do have NdarrayOrTensor.

[KumoLiu]

Thanks for the PR, few minor comments inline.

[wyli]

/build

[wyli]

Thanks, it looks good to me.