Fix bugs in IProgress<T> handling

[AArnott]

• Fixes Multiple IProgress<T> parameters in a single method signature doesn't work #371: Missing support for multiple IProgress<T> parameters on a single method
• Fix issues with IProgress handling in the MessagePackFormatter, including around storing and reusing a buffer after it has been recycled by making a copy of the token we need to use later.
• Fixes MessagePackFormatter serialization of IProgress<T> instances when the concrete type is known statically due to being a member on a data contract class.

Also extract some general helper methods to another class so we can reuse it in IAsyncEnumerable support.

[codecov-io]

Codecov Report

Merging #374 into master will decrease coverage by 0.05%.
The diff coverage is 85.48%.

@@            Coverage Diff             @@
##           master     #374      +/-   ##
==========================================
- Coverage   90.04%   89.98%   -0.06%     
==========================================
  Files          40       41       +1     
  Lines        3084     3116      +32     
==========================================
+ Hits         2777     2804      +27     
- Misses        307      312       +5

Impacted Files	Coverage Δ
src/StreamJsonRpc/JsonMessageFormatter.cs	93.05% <ø> (ø)	⬆️
...nRpc/Reflection/MessageFormatterProgressTracker.cs	95.16% <100%> (+1.82%)	⬆️
src/StreamJsonRpc/MessagePackFormatter.cs	92.72% <76.92%> (-0.39%)	⬇️
src/StreamJsonRpc/Reflection/TrackerHelpers.cs	78.57% <78.57%> (ø)

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