Geom api

[atbenmurray]

Fixes #7486.

This PR is an investigation of the API changes required to implement #7486. As it stands, it isn't yet intended to be the PR for the API changes, but it could turn into it if everyone is happy with it.

Description

API changes required to support raster and geometry tensors. So far this means:

• MapTransform minor API extension
• Spatial dictionary transforms (which may need no API extension)
• Spatial array transforms (which will likely need API extensions)

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.

[atbenmurray]

@KumoLiu @Nic-Ma @ericspod I think we can close this PR. I have a branch on my fork of MONAI that significantly updates this work.

[KumoLiu]

@atbenmurray Sure, close for now. And you can create any further pr later. Thanks