[Milestone] AssemblyLoader completed.

Details:
- Assembly Mgmt Service for loading now a separate interface, not intended for normal use.
- Assembly Loader work; implemented custom dictionary key and table.
- Assembly loading work.
- EventService completed.
- Moved assembly extensions to ModUtils.cs
- Work to event service.
NetworkService work
- Added ImpromptuInterfaces package.
- Networking Service work to support NetVars
- Event Service
- Added assemblies references package for script compilation. Updated Roslyn version for compatibility.
- Package Loading work.
Swap Harmony to HarmonyX
- More refactor conversion to FluentResults.
- Updated StylesService to return Results.
- Refactor of PackageService partially complete.
- Made IService.Reset() required to return a Result.
- Moved plugin/assembly related code to their own folder (same namespace).
- Updated interfaces to reflect the use of Result<T>.
- Partial refactor, incomplete.
- Added 'FluentResults' so we can stop using cursed Exception-based flow control in loading code.
- Added 'OneOf' nuget package: https://github.com/mcintyre321/OneOf
for the implementation of the Optional<T> pattern and complex discrete return types instead of cursed enums (see current AssemblyManager.cs).
- Reapplied old branch changes.

Barotrauma/BarotraumaClient/WindowsClient.csproj

@@ -15,6 +15,7 @@
     <InvariantGlobalization>true</InvariantGlobalization>
     <ApplicationManifest>app.manifest</ApplicationManifest>
     <WarningsAsErrors>;NU1605;CS0114;CS0108;CS8597;CS8600;CS8601;CS8602;CS8603;CS8604;CS8605;CS8606;CS8607;CS8608;CS8609;CS8610;CS8611;CS8612;CS8613;CS8614;CS8615;CS8616;CS8617;CS8618;CS8619;CS8620;CS8621;CS8622;CS8624;CS8625;CS8626;CS8629;CS8631;CS8632;CS8633;CS8634;CS8638;CS8643;CS8644;CS8645;CS8653;CS8654;CS8655;CS8667;CS8669;CS8670;CS8714;CS8717;CS8765</WarningsAsErrors>
+    <LangVersion>latest</LangVersion>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">