Add included files to the MSBuild Up-to-Date checks.

[jkoritzinsky]

Add included files to MSBuild up-to-date checks so incremental builds will update when the native headers change.

Clean up support for P2P dependencies that aren't referencing SharpGen.

[codecov]

Codecov Report

Merging #106 into master will decrease coverage by 2.11%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #106      +/-   ##
==========================================
- Coverage   58.61%   56.49%   -2.12%     
==========================================
  Files         150      150              
  Lines        9168     9172       +4     
  Branches     1123     1642     +519     
==========================================
- Hits         5374     5182     -192     
- Misses       3406     3410       +4     
- Partials      388      580     +192

Impacted Files	Coverage Δ
SharpGen/Parser/MacroManager.cs	98.3% <100%> (+0.09%)	⬆️
SharpGen/Generator/StructCodeGenerator.cs	63.63% <0%> (-36.37%)	⬇️
...harpGen/Generator/NativeInvocationCodeGenerator.cs	67.3% <0%> (-32.7%)	⬇️
SharpGen/Transform/ConstantManager.cs	67.53% <0%> (-20.78%)	⬇️
SharpGen/Generator/InterfaceCodeGenerator.cs	26.61% <0%> (-17.34%)	⬇️
SharpGen/Model/CsMarshalBase.cs	58.33% <0%> (-16.67%)	⬇️
SharpGen/Generator/RoslynGenerator.cs	69.52% <0%> (-12.39%)	⬇️
SharpGen/Generator/Marshallers/MarshallerBase.cs	40.95% <0%> (-11.27%)	⬇️
SharpGen/Model/CsMethod.cs	65% <0%> (-10%)	⬇️
SharpGen/Model/CsInterface.cs	86.95% <0%> (-8.7%)	⬇️
... and 27 more

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