error-stack expose Frame::type_id

[indietyp]

🌟 What is the purpose of this PR?

While developing deer (which heavily uses error-stack and Frames for errors), I often tried to get the current type contained in a Frame, before #1288 error-stack had a pub(crate) function with the same name (type_id). Even though error-stack no longer directly uses TypeId, I think it is still valuable to add the method for lower-level use cases outside of error-stack, to inspect the contained type easily.

This is entirely optional, one can also repeatedly call Frame::is<T>() for every expected type, but this isn't ideal, as it isn't very straightforward, nor ergonomic, or as performant as a simple lookup in a HashSet (or similar).

🔍 What does this change?

• exposes Frame::type_id

📜 Does this require a change to the docs?

Yes, the newly exposed method is documented.

❓ How to test this?

An additional test has been added to verify the behavior.

[codecov]

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[TimDiekmann]

I like the change. I think this can be really useful for downstream crates, which need more information on the Frames. Thank you!