Add future.v2_normalizeFormMethod flag

[brophdawg11]

Note: CI will fail until we point this to an RR experimental/prerelease version with these changes

Add a future flag to normalize/align useNavigation().formMethod. We want our API to behave like fetch() - it can accept lowercase or uppercase, but exposes the method back to you as a normalized uppercase method:

new Request("/", { method: "post" }).method === "POST" // true
new Request("/", { method: "POST" }).method === "POST" // true

So this means that both <Form method="post"> and <Form method="POST"> should result in useNavigation().formMethod === "POST".

We inadvertently shipped lowercase useNavigation values in RR 6.4, and only noticed the inconsistency when we went to deprecate useTransition in Remix which used uppercase. Therefore, we're putting this behind a future flag to avoid breaking apps, and in Remix v2 we'll move to uppercase as the default.

[changeset-bot]

🦋 Changeset detected

Latest commit: bb11865

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 18 packages

Name	Type
@remix-run/dev	Minor
@remix-run/react	Minor
@remix-run/server-runtime	Minor
@remix-run/testing	Minor
create-remix	Minor
@remix-run/css-bundle	Minor
@remix-run/cloudflare	Minor
@remix-run/deno	Minor
@remix-run/node	Minor
@remix-run/cloudflare-pages	Minor
@remix-run/cloudflare-workers	Minor
@remix-run/architect	Minor
@remix-run/express	Minor
@remix-run/netlify	Minor
@remix-run/vercel	Minor
@remix-run/serve	Minor
remix	Minor
@remix-run/eslint-config	Minor

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[brophdawg11]

Cherry-picked the new future flags docs from main into here so I could add the new flag to them

[github-actions]

🤖 Hello there,

We just published version v0.0.0-nightly-4d86674-20230321 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

Thanks!