Move IJsonRpcMessageBufferManager into Reflection namespace

[AArnott]

Fixes #380

[codecov-io]

Codecov Report

Merging #381 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #381   +/-   ##
=======================================
  Coverage   89.92%   89.92%           
=======================================
  Files          41       41           
  Lines        3117     3117           
=======================================
  Hits         2803     2803           
  Misses        314      314

Impacted Files	Coverage Δ
src/StreamJsonRpc/PipeMessageHandler.cs	91.35% <ø> (ø)	⬆️
src/StreamJsonRpc/JsonRpc.cs	93.16% <ø> (ø)	⬆️

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