Fix accessing headers in progressively enhanced form actions (#74196)
When scoping the `requestStore` to dynamic renders in #72312, we missed
the case when a server action is invoked before hydration is complete.
This leads to an error when a server action tries to read headers,
cookies, or anything else that requires the presence of the
`requestStore`.
This fixes that for both the Node.js and Edge runtimes. It also appears
that progressively enhanced form actions did not work at all before in
the Edge runtime due to a missing `await` of `decodeFormState`.
fixes #73992
closes NAR-55