Support SSLKEYLOGFILE in Release builds

[rzikm]

Closes#37915.

This PR unifies existing SSLKEYLOGFILE exporting between SslStream and QuicConnection to use same shared code, and enables the feature in Release builds of libraries. This makes the feature available to consumers without needing to compile Debug builds of .NET Runtime.

Note that the SSLKEYLOGFILE feature is currently supported for:

OS	SslStream	QuicConnection
Windows	Not possible	Yes
Linux	Yes	Yes
OSX	Not possible?	Yes*

*MsQuic is not yet officially supported on OSX, but once it is, no changes should be necessary from .NET side.

For security concerns, in addition to setting SSLKEYLOGFILE environment variable, setting System.Net.EnableSslKeyLogging AppContext switch to true is required. This can be done either via code

AppContext.SetSwitch("System.Net.EnableSslKeyLogging",true);

or via {project}.runtimeconfig.json

{
"runtimeOptions": {
"configProperties": {
"System.Net.EnableSslKeyLogging": true
}
}
}

Debug runtime libraires (= local development builds of .NET Runtime) don't require the AppContext switch for the feature.

[ManickaP]

LGTM modulo few small comments. Thank you!

[wfurt]

LGTM in general.

[rzikm]

CI Failures are unrelated