Enforce timeout on network read/writes.

[kasobol-msft]

Problem
This is to address situation when response parsing hangs on reading response stream indefinitely here https://github.com/dotnet/runtime/blob/5d5c36bb9e887cfe50913840ba96985da113640f/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlTextReaderImplAsync.cs#L1195 .

The reproduction scenario : https://gist.github.com/brettsam/85950a65fc50da044dee6ec242944895

Solution
The solution is inspired by V12 where timeouts are enforced by wrapping response stream ReadTimeoutStream .
Additionally ByteCountingStream wrapper has been fixed - absent override were causing it to use default implementation - effectively loosing cancellation token and not passing it into http/network stack.

Extra
Additionally WithCancellation extension has been improved to mark exceptions thrown by abandoned tasks as handled.

Testing
I've been running reproduction scenario and observed that after changes it didn't hang but threw cancellation exception.

[seanmcc-msft]

Have you ran tests on all 3 platforms (Core 1.3, Core 2.0, and Net Framework)?

[kasobol-msft]

Have you ran tests on all 3 platforms (Core 1.3, Core 2.0, and Net Framework)?

@seanmcc-msft I've run tests on all 3 platforms on branch and on master. No regression comparing to master.