[HTTP/3] Loopback server should dispose underlying QUIC connection

[geoffkizer]

The logic to do this is currently disabled: https://github.com/dotnet/runtime/blob/main/src/libraries/Common/tests/System/Net/Http/Http3LoopbackConnection.cs#L57

We should re enable this and fix tests accordingly.

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Issue Details

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The logic to do this is currently disabled: https://github.com/dotnet/runtime/blob/main/src/libraries/Common/tests/System/Net/Http/Http3LoopbackConnection.cs#L57

We should re enable this and fix tests accordingly.

Author:	geoffkizer
Assignees:	-
Labels:	area-System.Net.Http, test bug
Milestone:	7.0.0

[karelz]

Triage: We disabled the behavior to make tests pass on all versions of HTTP -- we will have to review the failures again once we work on this.

[karelz]

Triage: Try it and see what it does. If there are too many issues, we are fine with Future.

[ManickaP]

Let's revisit this while working on CloseAsync/DisposeAsync in #68902