We currently assume that any functions passes as props may be event
handlers or effect functions, and thus don't check for side effects such
as mutating globals. However, if a prop is a function that returns JSX
that is a sure sign that it's actually a render helper and not an event
handler or effect function. So we now emit a `Render` effect for any
prop that is a JSX-returning function, triggering all of our render
validation.

This required a small fix to InferTypes: we weren't correctly populating
the `return` type of function types during unification. I also improved
the printing of types so we can see the inferred return types.

---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/33647).
* #33643
* #33650
* #33642
* __->__ #33647

Previously, the compiler would incorrectly attempt to compile nested
components/hooks defined inside non-React functions. This would lead to
scope reference errors at runtime because the compiler would optimize
the nested React function without understanding its closure over the
parent function's variables.

This PR adds detection when non-React functions declare components or
hooks, and reports a clear error before compilation. I put this under a
new compiler flag defaulting to false. I'll run a test on this
internally first, but I expect we should be able to just turn it on in
both compiler (so we stop miscompiling) and linter.

Closes #33978

Playground example:
https://react-compiler-playground-git-pr34305-fbopensource.vercel.app/#N4Igzg9grgTgxgUxALhAejQAgAIDcCGANgJYAm+ALggHIQAiAngHb4C2xcRhDAwjApQSkeEVgAcITBEwpgA8jAASECAGswAHSkAPCTAqYAZlCZwKxSZgDmCCgEkmYqBQAU+AJSZgWzJjiSwAwB1GHwxMQQYTABeTBdPaIA+Lx9fPwCDAAt8JlJCBB5sphsYuITk7yY0tPwAOklCnJt4gG5U3wBfNqZ2zH4KWCqAHmJHZ0wGopto4CK8gqmEDsw0RO7O7tT+wcwQsIiYbo6QDqA

I happened to notice that I forgot to cache playwright in
run_devtools_e2e_tests, so it would try to install it every time which
can randomly take a while to complete (I'm not sure why it's not
deterministic, but the dependencies appear to be installed
inconsistently across multiple workflows).

This PR adds the same cache we use for other steps that use playwright,
which should shave off some time from this workflow when the cache is
warm.

Additionally I omitted the standalone install-deps command as it appears
to be redundant and adds a lot of extra time to CI, due to the fact that
it installs many unrelated dependencies.

---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/34320).
* #34321
* __->__ #34320