Add NetworkError.TimedOut, rename Unknown to Other

[antonfirsov]

• Adds NetworkError.TimedOut
• Renames Unknown to Other assuming my proposal gets accepted, will revert if not
• Improves exception message

Will add a case for TimedOut as soon as the Connection PR gets merged. (Based on local test it gets translated fine.)

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[antonfirsov]

/cc @scalablecory @geoffkizer

[geoffkizer]

@antonfirsov The failure in System.Net.Requests.Tests looks related, though I'm not sure how your change would affect this... can you take a look?

[geoffkizer]

That also could have been caused by the recent ConnectionFactory PR.

[ManickaP]

The problem is in missing mapping in https://github.com/dotnet/runtime/blob/master/src/libraries/System.Net.Requests/src/System/Net/WebException.cs#L74

@antonfirsov if you're afk, I can try to fix it.

I think this might be fixed by #40880. Since we have NetworkException bubbling out of HttpClient here and we should be mapping it into HttpRequestException, which already is properly handled by WebException mapping.

[ManickaP]

/azp run runtime

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[antonfirsov]

/azp run runtime-libraries outerloop

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[antonfirsov]

/azp run runtime

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[antonfirsov]

/azp run runtime

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[antonfirsov]

/azp run runtime-libraries outerloop

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[antonfirsov]

OuterLoop test failures are unrelated. Opened new issues: #40926, #40927