Adopt unstable_stream API for internal middleware implementation

[brophdawg11]

This is a decent-sized internal refactor for middleware logic, aligning code for consistency across middleware and non-middleware flows as well as RSC and non-RSC flows.

We used to have an unstable_respond API on the static handler which was basically in charge of converting a StaticHandlerContext -> Response in the leaf next() so we could bubble a Response back up the middleware chain.

When RSC came around, we realized this was insufficient for server actions because we had no way to run middleware before the server action and then process the server action and the loaders for the revalidating RSC render as part of the leaf next(). To solve that we added an unstable_stream alternative alongside unstable_respond which allowed us to opt-0into this more advanced functionality in the RSC work without causing potential regressions in non-RSC middleware code flows using unstable_respond.

Now that RSC is out (unstable) and we're getting closer to stabilizing middleware, it's time to convert existing usages of unstable_respond over to the new API and get rid of it.

This PR also renames it to unstable_generateMiddlewareResponse for clarity and does a bunch of code cleanup for better sharing of code across middleware and non-middleware flows.

[changeset-bot]

🦋 Changeset detected

Latest commit: bc1f18b

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

This PR includes changesets to release 11 packages

Name	Type
react-router	Patch
@react-router/architect	Patch
@react-router/cloudflare	Patch
@react-router/dev	Patch
react-router-dom	Patch
@react-router/express	Patch
@react-router/node	Patch
@react-router/serve	Patch
@react-router/fs-routes	Patch
@react-router/remix-routes-option-adapter	Patch
create-react-router	Patch

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[github-actions]

🤖 Hello there,

We just published version 7.8.0-pre.0 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!

[github-actions]

🤖 Hello there,

We just published version 7.8.0 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!