Switch default to to retain order of incoming RPC invocations

[AArnott]

Closes #521

[codecov-commenter]

Codecov Report

Merging #525 into master will decrease coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #525      +/-   ##
==========================================
- Coverage   89.28%   89.18%   -0.11%     
==========================================
  Files          51       51              
  Lines        4059     4076      +17     
==========================================
+ Hits         3624     3635      +11     
- Misses        435      441       +6     

Impacted Files	Coverage Δ
src/StreamJsonRpc/JsonRpc.cs	92.50% <100.00%> (+<0.01%)	⬆️
src/StreamJsonRpc/WebSocketMessageHandler.cs	87.03% <0.00%> (-10.34%)	⬇️
...pc/Reflection/MessageFormatterDuplexPipeTracker.cs	94.25% <0.00%> (-1.15%)	⬇️
src/StreamJsonRpc/MessageHandlerBase.cs	100.00% <0.00%> (+1.21%)	⬆️

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