[v3] h5py compat methods on Group

[jhamman]

This PR adds the h5py compat methods to the Zarr Group API from v2.

The plan described in #1583 was to remove these but after looking into it, a bit more, I came to the conclusion that require_group and require_dataset are actually pretty useful. I'm open to adding deprecation warnings to create_dataset and require_dataset (perhaps replacing the latter with require_array) if we want to phase out the h5py specific language.

closes #1597

TODO:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in docs/tutorial.rst
• Changes documented in docs/release.rst
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[joshmoore]

In general, big 👍 for the compatibility. cc: @clbarnes of https://github.com/clbarnes/h5py_like fame in case there are any lessons learned, etc. that we should take into account.

[d-v-b]

I'm open to adding deprecation warnings to create_dataset and require_dataset (perhaps replacing the latter with require_array) if we want to phase out the h5py specific language.

+1 to this, ultimately we shouldn't use the term "dataset". But for short-term hdf5 compatibility this PR looks good.

[jhamman]

In general, big 👍 for the compatibility. cc: @clbarnes of https://github.com/clbarnes/h5py_like fame in case there are any lessons learned, etc. that we should take into account.

I'm going to go ahead and merge this but happy to take feedback from @clbarnes here or in #1597.

[clbarnes]

Nothing specific to say, just happy if h5py_like was of any use! Definitely agree on throwing PendingDeprecationWarnings whenever these short-term compatibility measures are used, otherwise you'll never be rid of them.