Implement backwards-compatible shape and dims with Ellipsis support

[twiecki]

Here is what I did:
Create a diff between #4693 and #4667 and stage that diff onto a branch off of #4693 (no conflicts!). I then ran git commit -p and only selected those that seemed necessary here. Mostly there were some changes to tests that changed size to shape I did not commit.

Remember: Before merging still need to change author to @michaelosthege.

[twiecki]

I think this looks great!

[twiecki]

Just changed base to v4, not sure why we're getting conflicts there as #4693 was merged into v4?

[michaelosthege]

After rebasing I'm now pushing this branch commit by commit, so we get CI results on all of them.

[twiecki]

Let me try and finish up the shape.py PR soon.

…

On Sun, May 23, 2021, 14:39 Oriol Abril-Pla ***@***.***> wrote: +1 on merging, further improvement and simplification can come in follow-up PRs, I don't think there is discussion in terms of functionality anymore so future PRs should not have any visible effect. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#4696 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAFETGEVCRWV3P5MVXT5RUDTPDZRNANCNFSM44342NCA> .

[michaelosthege]

As we decided in todays lab meeting is rebased this branch so we can merge it.

There were quite a few git conflicts, as anticipated, but it looks like nothing broke.

[twiecki]

OK good to merge from my end!

…

On Fri, Jun 4, 2021, 19:01 Michael Osthege ***@***.***> wrote: As we decided in todays lab meeting <https://github.com/pymc-devs/pymc3/wiki/Project-Meeting-Minutes#friday-june-4-2021> is rebased this branch so we can merge it. There were quite a few git conflicts, as anticipated, but it looks like nothing broke. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#4696 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAFETGHAFFJYKZERNMY25OTTREBHLANCNFSM44342NCA> .

[twiecki]

Thanks to everyone who helped get this over the finish line, especially the herculean efforts of @michaelosthege! Also thanks for helpful review from @brandonwillard, @ricardoV94, @OriolAbril and everyone else.