Expose UrlForm.parse and UrlFormDecodeError

[BalmungSan]

At work, we built our own SimpleUrlFormProtocol and the implementation mostly reuses what smithy4s already has.
However, we had to use runtime reflection to access these bits. Which, IMHO, could (should?) be public.

Let me know what you think and if I should do something else.

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PR Checklist

• Added unit-tests (already there)
• Added documentation
• Updated changelog

[CLAassistant]

All committers have signed the CLA.

[kubukoz]

oops, didn't check the description earlier, thought it was such an obvious change 🤪

I'd say we should update the changelog. Don't know if there's any documentation about forms so far.

[BalmungSan]

@kubukoz added some docs and the CHANGELOG entry.
Let me know if there is any feedback about those or if I missed something else :)

[kubukoz]

Looks like it's failing formatting, can you run sbt formatAll and commit?

[dhpiggott]

At work, we built our own SimpleUrlFormProtocol

Interesting! What does it do/what is it used for? Is it URL form data in and JSON out by any chance, or something else?

[mazurio]

@dhpiggott We use this for OKTA (Token Exchange) - that endpoint uses x-www-form-urlencoded that accepts grant_type=client_credentials and returns an access_token with scope etc.