[Feature] include pending requests in trace

[yury-s]

But one small problem remains: there is no pending request in the Trace viewer → Network tab. Could you please add any network activity, not just completed?

Originally posted by @Diokuz in #15567 (comment)

[aldenquimby]

My team recently hit this issue. We had a test timeout because an API request was slow, and it took us a while to track down because we assumed traces would include pending requests that hadn't received a response before a test timed out.

@yury-s I'd be glad to help with a PR for this. Do you already have thoughts on implementation? Could you point me in a starting direction? Thank you!

[iguptarav]

In my experience of running playwright e2e tests 24*7 in AWS and locally, pending requests are the number one reason for impossible to track down test failures. I am really surprised there hasn't been more push towards surfacing this crucial information.