Fix Hang on when GetRequestStreamAsync

[liveans]

Fixes #113398.

This is a regression, we should probably back port this to .NET 9.0

[Copilot]

Pull Request Overview

This PR addresses a regression that caused GetRequestStreamAsync to hang by introducing timeout logic in the internal request stream retrieval and propagating underlying exceptions. Key changes include:

• Wrapping the stream retrieval in a Task.WhenAny and WaitAsync-based timeout mechanism.
• Propagating exceptions when the underlying send request task fails.
• Adding a new unit test for requests with buffering disabled and an invalid host to verify correct exception handling.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/libraries/System.Net.Requests/src/System/Net/HttpWebRequest.cs	Modified InternalGetRequestStream to use timeout logic and propagate exceptions from SendRequest.
src/libraries/System.Net.Requests/tests/HttpWebRequestTest.cs	Introduced a new test to ensure that an invalid host with buffering disabled causes the expected exception.

[liveans]

The one thing that I've noticed is that, when user is using async path already they should implement their own timeout mechanism according to the doc: HttpWebRequest.Timeout - Remarks

Not sure, if we should stick to that behavior and limit propagating of Timeout here.

[ManickaP]

WaitAsync will not cancel / stop the underlying tasks. What happens with them? I think this will at minimum generate unobserved exceptions.
It would be better to pass the timeout to the tasks themselves via cancellation token and them catch the exception and remap to TimeoutException if necessary. (we do this a lot around HttpClient).