Add TransmissionCompletedSize ETW event

[MokoSan]

Updated implementations of IJsonRpcMessageHandler to emit a new event including the size of payload.

These implementations include those of:

1. HeaderDelimitedMessageHandler.cs
2. LengthHeaderMessageHandler.cs

[ghost]

All CLA requirements met.

[codecov-commenter]

Codecov Report

Merging #488 into master will decrease coverage by 0.08%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master     #488      +/-   ##
==========================================
- Coverage   90.64%   90.55%   -0.09%     
==========================================
  Files          50       50              
  Lines        3838     3844       +6     
==========================================
+ Hits         3479     3481       +2     
- Misses        359      363       +4     

Impacted Files	Coverage Δ
src/StreamJsonRpc/JsonRpcEventSource.cs	6.97% <0.00%> (-0.35%)	⬇️
src/StreamJsonRpc/HeaderDelimitedMessageHandler.cs	85.63% <50.00%> (-0.42%)	⬇️
src/StreamJsonRpc/LengthHeaderMessageHandler.cs	97.22% <50.00%> (-2.78%)	⬇️

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