Add Error Boundary to useTransition API docs

[kmiddleton14]

Error Boundary now works in React canary with useTransition API and displays the fallback. This PR adds documentation with a simple usage example.

Note that we want to prevent the error dialog from displaying in the Sandpack when we throw an error so that we can show the error boundary fallback.

Preview link

Monosnap.screencast.2023-10-17.15-23-20.mp4

[github-actions]

Size changes

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[sophiebits]

I'm looking at this again and I'm worried this isn't realistic enough to be helpful. Do we really expect people to throw on purpose directly in a transition? Or should we be trying to explain what happens when there is an unhandled error.

Assuming the latter (which had been my assumption), can we make the code call some a function with a real product action name that ends up throwing? Like function addComment() {}. It can fail unconditionally but what we should be teaching IMO is how errors in normal code bubble up when that code fails.

[kmiddleton14]

@sophiebits yes your assumption is correct it was more of a tool to demonstrate what happens with an unhandled error. That's a good point and I can update to be a more product specific example

[kmiddleton14]

Not ready for review - had some merging issues and will resolve first