Create ModuleLoader.Abstractions

[ztanczos]

• Create ModuleLoader.Abstractions package under src which expose the types required by both the Module Loader and the FDC3* related packages.
• Add unit tests

[codecov]

Codecov Report

Merging #373 (f05a0b5) into main (90e0865) will decrease coverage by 0.24%.
The diff coverage is 43.24%.

@@            Coverage Diff             @@
##             main     #373      +/-   ##
==========================================
- Coverage   77.41%   77.18%   -0.24%     
==========================================
  Files         161      164       +3     
  Lines        5438     5475      +37     
  Branches      233      233              
==========================================
+ Hits         4210     4226      +16     
- Misses       1227     1248      +21     
  Partials        1        1              

Files	Coverage Δ
...poseUI.ModuleLoader.Abstractions/StartupContext.cs	92.30% <92.30%> (ø)
...omposeUI.ModuleLoader.Abstractions/StartRequest.cs	66.66% <66.66%> (ø)
...mposeUI.ModuleLoader.Abstractions/LifetimeEvent.cs	0.00% <0.00%> (ø)