[Feature] Better documentation for yarn constraints command

[broofa]

• I'd be willing to implement this feature (contributing guide)
• This feature is important to have in this repository; a contrib plugin wouldn't do

Describe the user story

Long-time yarn user, but first time diving into the yarn constraints command (JS-based version in yarn@4, not the old Prolog version). My first impression of the docs (https://yarnpkg.com/features/constraints) is that they're enough to just barely get started, but are missing the key information to allow a developer to actually do anything useful.

Specifically, it'd be nice to have answers to the following questions ...

• What is the API of the Yarn object passed to the constraints() method?
• What is the "shape" of the arguments passed to the various Yarn.* methods? ("The examples show you can pass an object with an ident string property. What are the allowed patterns / values for that property? What other properties can be provided?)
• What is the API of the various sub-objects w/in the Yarn API? What are the return values for methods like dependencies and workspaces? What is the API for those things?
• What is the recommended way of surfacing a constraint violation? (E.g. "Should I throw an Error? If so, what type?")

After a big of digging, I found the following resources that I suspect developers would find helpful. These aren't really documentation per-se, but they at least provide some information that answers some of the above questions:

• Source for the TS types in @yarnpkg/types
• yarn project's own yarn.config.cjs (provides more complex examples, that I'm guessing have driven much of the existing Yarn API requirements?)

Adding examples for the following would be helpful:

• Handling a dependency constraint violation (call dependency.error()?)
• Handling a workspace constraint violation (call workspace.error()?)