HTTP/3 RequestHeadersTimeout

[JamesNK]

Adds RequestHeadersTimeout support to HTTP/3

Addresses #29702

(this PR is still rough. Creating it early to ask questions)

The HTTP/3 approach doesn't use ITimeoutControl for this feature because multiple time controls would be required per connection, and checking them in Tick() would require locking the streams dictionary, foreaching over the values, and evaluating each timeout control.

The approach used instead is like HTTP/2's drain stream queue. New streams are added to a concurrent queue, and each tick streams are checked to see whether they have received headers and are in a "started" state.

I made RequestHeadersTimeout apply to both request streams and control streams. They each have the same attack vector: creating streams from the client and then never using them. Control streams use the same timeout to receive the control stream header.

A future possible optimization is to check whether the first read of an incoming stream completes immediately, and the first HEADERS frame or control stream frame header is immediately available. If it is then the stream can skip being added to the startingStreamsQueue.

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V3: On connection tick, the stream dictionary is locked and iterated over to check for streams (both request streams and inbound control streams) to see if they have received a header.

I chose not to use TimeoutControl here to avoid each stream requiring its own TimeoutControl for this one thing AND the connection having a timeout control which streams also use to track data rates.

This PR starts to unify how inbound control streams and request streams are acted on. They are both put into the streams dictionary so the same logic is applied to streams from the client:

• Checking a stream has started
• Aborting streams when connection aborts

@halter73 and I discussed the foreach in the lock, and while it isn't ideal:

• It happens once per second
• Little happens in it
• Default QUIC stream limit for requests is 100 so it is a bounded collection
• Compared to other locks, it will have much less contention. For example, the HTTP/2 level connection locks its framewriter multiple times per request and does much more complex work inside the lock.