Add <form> Component reference documentation

[mattcarrollcode]

Add initial reference documentation for the <form> Component

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📦 Next.js Bundle Analysis for react-dev

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The following page changed size from the code in this PR compared to its base branch:

Page	Size (compressed)	First Load
/[[...markdownPath]]	78.83 KB (🟡 +12 B)	182.57 KB

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[elicwhite]

This is super cool! I appreciate the examples. As this gets closer to shipping we'll want to figure out more user friendly and less code-centric examples of course. I'm sure you have a list of things you want to do and I jumped the gun on reviewing this anyways 😀

[eps1lon]

FYI:

• stable preview link for latest changes for branches on upstream (such as this branch): react-dev-git-<branch-name>-fbopensource.vercel.app
• stable preview link for latest changes for branches forks: react-dev-git-fork-<username>-<branch-name>-fbopensource.vercel.app

More details in https://vercel.com/docs/deployments/generated-urls and https://github.com/orgs/vercel/discussions/970#discussioncomment-3918729 for forks.

[mattcarrollcode]

In person code review notes with @lunaleaps :

• refer the funciton passed to the action prop as a "action"
• rephrase "form action" to a "the action passed to form"
• useFormState error example: why do we need to use useFormState? call out that if you use a client action that calls a server action that returns and error disables progressive enhancement

[davidmccabe]

This is great.

[lunaleaps]

Love this! Thanks for all the updates. I have some suggestions -- mostly spelling and occasional sentence re-ordering but those aren't blocking!

I think the only blocking thing is the error boundary example not working