[dev] Define request ID for RSC requests on the client (#84605)
Previously, we defined a request ID for RSC requests on the server. The
request ID is used to tag debug information sent via WebSocket to the
client, which then routes those chunks to the debug channel associated
with this ID.
However, this meant that the client had to await the server response to
retrieve the request ID from the response headers, before we could pass
the response (and the debug channel) to React.
For #84580, we want to pass the response promise directly to React, to
accurately show timing information about the request in the React
DevTools. To achieve this, we now define the request ID on the client,
and send it to the server via a request header. This means that the
client can create the debug channel immediately, without waiting for the
server response.
closes NAR-426
