Purely demonstrating type checking behaviour for vega#3552 (comment)

Revisting these I found it confusing that they were defined like (A, B, B, A).
They are now (A, A, B, B) so it is clearer how they are linked

Aiming to get all of these to pass, without breaking anything else.
**CI fail expected**

…-compliant

Can't define this in `OperatorMixin`, as `Expression` uses `{"type": "string"}`

Added a lot of notes here, since I was surpised `Then` would not be allowed in the cases I had planned originally

We're using a feature that didn't make it into `3.13` yet https://peps.python.org/pep-0728/

The warning raised by `pyright` here was actually quite helpful.
Essentially, a shorthand string is never allowed here

vega#3552 (comment)

We now provide more precise errors identifying exactly which call produced the issue.
Previously, the `.then("min(foo):Q")` was silently allowed - but later rejected in `.otherwise()`.

I'm fairly sure this is fixed in another branch, so leaving this here for less of a conflict
https://github.com/vega/altair/pull/3547/files#diff-bbe4e187b18d242a366c820d023afd89041759cb96e4ec66c3f34559a72c2f9d

No longer inherited

vega#3567 (comment)

Removes the need for hardcoding restrictions in multiple places

…edDict`)

- Adds some more consistency between `condition` and `when-then-otherwise`
- 1 less thing to think about

This isn't a runtime concern, just to satisfy typing

Mostly pushing this as an experiment.
Shortens signatures, but there is a cost to the indirection

vega#3567 (comment)