Instead of building PSReadLine from this repo, pull it from the gallery using nuget cache.
This pulls v2.0 of PSReadLine which does have documented breaking changes from v1.2, but the risk is small - the features that have changed are typically only used in a profile and aren't used all that often anyway.
Fix#996
Hardcodes version of modules pulled from PSGallery
The code in `AssemblyLoadContext.dll` doesn't need to be in a separate DLL anymore.
S.M.A.dll depends on `AssemblyLoadContext.dll`, so keeping that code out of S.M.A.dll doesn't help make S.M.A smaller size or less dependent. So the code in `AssemblyLoadContext.dll` is moved to `S.M.A.dll` and then we remove `AssemblyLoadContext.dll`.
The changes are:
- Move `CorePsAssemblyLoadContext.cs` to `src\S.M.A\CoreCLR\`
- Update `CorePsAssemblyLoadContext.cs` to get the test took moved to `Utils.InternalTestHooks` and update tests
- Update `build.psm1` and `.csproj` accrodingly
- Update `pwrshcommon.cpp` to remove `AssemblyLoadContext.dll` from the TPA list.
- `S.M.A.AssemblyExtensions` is removed as `PackageManagement` has finished their move to .NET Core 2.0. (I will work with Bryan to get the latest version uploaded to powershell-core)
