Actions: auto-redirect action response to avoid "confirm form resubmission" dialog

[bholmesdev]

Changes

This change adds automatic redirects when an action is called. This follows Laravel's POST/redirect/GET pattern to avoid a "confirm form resubmission" dialog and remove the ?_astroAction param from the rendered result.

See the changeset for usage instructions.

• Persist action data in a cookie. This cookie is not encrypted. We are investigating a general encryption strategy for Astro as part of Astro Islands: Encrypt server islands props #11535. If Astro adopts an encryption key as part of the runtime, we will revisit encryption of the action result cookie.
• Redirect to referrer on error, and the url.pathname on success.
• If an action cookie is present, populate getActionResult with the cookie JSON. Delete after the request has been fulfilled.

Testing

Update integration tests to follow an expected redirect.

Docs

Updated RFC docs with new guide: https://github.com/withastro/roadmap/blob/actions/proposals/0046-actions.md#call-actions-from-an-html-form

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[bluwy]

The code looks good to me. I suppose we want to wait for the docs change before merging?

[ematipico]

@bholmesdev is there a chapter in the RFC I can look at before reviewing the code?

[bholmesdev]

@ematipico Thanks for flagging that! I just finished a new guide on the RFC docs: https://github.com/withastro/roadmap/blob/actions/proposals/0046-actions.md#call-actions-from-an-html-form

Writing out examples actually helped me find a design flaw. I decided the cookie should not be cleared on success. Otherwise, the action result data would disappear on a refresh.