API, Core: add multi-arg transform and add zOrder as the first one

[advancedxy]

Per discussed, this is the API/Expression part of multi-arg transform.

It's still working in progress as UTs are not added yet and more importantly some of the API definition doesn't seem alright.

I'm sending it early so that anyone who is interested could give some valuable feedback while I'm continue refining it.

[advancedxy]

@szehon-ho Thanks for taking #9661 over and sorry for the late response. I was busy finishing a big internal feature last week.

I extracted the API/Core part from previous POC PR and made some refinements. While doing that, I went ahead and added a poc implementation of ZOrder transform which you might be interested in? The zOrder transform helps that we can actually build and persist a multi-arg transform in the tests.

Currently, I am not satisfied with API part. The PartitionField part is fine, however the Unbound/Transform/Predicate part doesn't seem right. Any feedback will be appreciated.

Hopefully this part of work would unblock your work on multi-arg geo transforms.