improve debuging HTTP/2 tests

[wfurt]

I bump to two issue while working on #94112

1. I was using the SSLKEYLOG environment so I can decrypt TLS and peek at the HTTP/2 exchange.
   However, often the sessions keys were not there and I failed to decrypt the transaction. It seems like when the handshake happens and the process exist immediately not everything is written. Adding Flush seems to fix this.
   It may come with some perf cost but this is Debug only feature so it should not matter as much.

2. The issue would happen only when running whole test suite. I wanted to instrument the test to spit out the IPEndPoints so I can find the connection among many in the capture file. So I added ToString that can giver me something like
   Http2LoopbackConnection 127.0.0.1:42543 <-> 127.0.0.1:60302

with that I can set filer in Wireshark as tcp.port==42543 and get

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Issue Details

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I bump to two issue while working on #94112

1. I was using the SSLKEYLOG environment so I can decrypt TLS and peek at the HTTP/2 exchange.
   However, often the sessions keys were not there and I failed to decrypt the transaction. It seems like when the handshake happens and the process exist immediately not everything is written. Adding Flush seems to fix this.
   It may come with some perf cost but this is Debug only feature so it should not matter as much.

2. The issue would happen only when running whole test suite. I wanted to instrument the test to spit out the IPEndPoints so I can find the connection among many in the capture file. So I added ToString that can giver me something like
   Http2LoopbackConnection 127.0.0.1:42543 <-> 127.0.0.1:60302

with that I can set filer in Wireshark as tcp.port==42543 and get

Author:	wfurt
Assignees:	wfurt
Labels:	area-System.Net.Http, test-enhancement
Milestone:	9.0.0