Improve grpc-dotnet debugging

[JamesNK]

This PR significantly improves the debugging experience of gRPC calls. Changes have been applied in many places. There are before and after screenshots of each.

ServerCallContext

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Server StreamReader

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Server StreamWriter

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Client call

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Client StreamReader

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Client StreamWriter

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Metadata

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[mgravell]

Ignore previous comments: you'd already done what I suggested, I just misread the code