Propagate the server trace to Remix 3 page loads #25137

Browser page loads in Remix 3 start a new trace. The server middleware already adds a Server-Timing entry to HTML responses for the route pattern; add sentry-trace and baggage entries the same way, as the Remix 2 SDK and Nitro do. The browser SDK reads Server-Timing for page loads already, so no client change should be needed.