[release/7.0] Unload MsQuic after checking for QUIC support to free resources.

[github-actions]

Backport of #74749 to release/7.0, closes#74629.

/cc @rzikm

Customer Impact

When using HttpClient, we also check whether the running platform supports QUIC (to enable HTTP3). However, the way we are checking QUIC support causes many threads to be allocated in the native MsQuic library (2* number of logical cores). This causes unnecessary resource increase even if the process does not end up using HTTP3 at all (HTTP3 is opt-in). This would therefore cause regression in memory usage when upgrading to .NET 7 in such cases.

Affected platforms include Windows 11, Windos Server 2022, many Linux platforms with msquic package installed.

Testing

Functional tests suite passes as part of the CI, resource consumption was checked manually.

Risk

Low, the fix consists of gracefully unloading MsQuic library from the process after checking QUIC support. The library is reloaded only when actually needed.

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Issue Details

---

Backport of #74749 to release/7.0

/cc @rzikm

Customer Impact

Testing

Risk

IMPORTANT: Is this backport for a servicing release? If so and this change touches code that ships in a NuGet package, please make certain that you have added any necessary package authoring and gotten it explicitly reviewed.

Author:	github-actions[bot]
Assignees:	-
Labels:	area-System.Net
Milestone:	-

[carlossanlop]

The CI was down yesterday for maintenance. Only 5 checks were executed while that happened. I'm closing and reopening this PR so the full CI runs.

[rzikm]

Putting this on hold until we investigate #74952

[rzikm]

There is a problem which manifests on Debian11+Docker+ARM64 with this change, we would need changes in MsQuic as well, so I am closing this for now.