We're going to use this branch to release a minor 18.3 release based off
the published 18.2 release revision. This will include some additional
warnings to assist in upgrading to React 19, but no behavior changes
compared to 18.2.

I bumped the React version to 18.3 and all the other packages by a patch
revision (since we're not going to update anything in those).

…e) (#25383)

## Summary
 
Alternate to #25334 without any
prod runtime changes i.e. the proposed codemod in
https://github.com/reactjs/rfcs/blob/createlement-rfc/text/0000-create-element-changes.md#deprecate-string-refs-and-remove-production-mode-_owner-field
would not work.

## How did you test this change?

- [x] CI
- [x] `yarn test` with and without `warnAboutStringRefs`

This improves the error message a bit and ensures that we recommend
putting the key first, not last, which ensures that the faster
`jsx-runtime` is used.

This only affects the modern "automatic" JSX transform.

…25699)

This also fixes a gap where were weren't warning on memo components.

This backports a deprecation warning for legacy context, even when
Strict Mode is not enabled.

I didn't bother to update all the tests because the tests are in such
a different state than what's on `main`, and on `main` we already
updated the tests accordingly. So instead I silenced the warnings in
our test config, like we've done for other warnings in the past.

This commit adds warnings indicating that `renderToStaticNodeStream`
will be removed in an upcoming React release. This API has been legacy,
is not widely used (renderToStaticMarkup is more common) and has
semantically eqiuvalent implementations with renderToReadableStream and
renderToPipeableStream.

landed in main in #28872 
changed the warning to match renderToNodeStream

Previously, the `refs` property of a class component instance was
read-only by user code — only React could write to it, and until/unless
a string ref was used, it pointed to a shared empty object that was
frozen in dev to prevent userspace mutations.

Because string refs are deprecated, we want users to be able to codemod
all their string refs to callback refs. The safest way to do this is to
output a callback ref that assigns to `this.refs`.

So to support this, we need to make `this.refs` writable by userspace.

Adds a deprecation warning to ReactDOMTestUtils.renderIntoDocument,
which is removed in version 19.

Also backports the deprecation warning for ReactDOMTestUtils.act.

This is removed in version 19. We already warned inside of Strict Mode
but this adds the warning everywhere.

This should have been deprecated in 18.0 alongside the other legacy
DOM APIs like render().