* update to latest package references
* update runtime framework
* update sdk
* automatically read NuGet package dependency info from csproj, where version info is fully qualified
* update file.wxs
The main purpose of this was to enable full symbols for windows release build.
Also makes explicit where we are optimizing and where we are not optimizing due to https://github.com/dotnet/corefx/issues/29700
* Build Update
- Change `TargetFramework` to `netcoreapp2.1` and removed unnecessary `RuntimeFrameworkVersion` from `PowerShell.Common.props`
- Update dotnet SDK to 2.1.300-rc1-008662
- Update `TypeGen` target in `Build.psm1` to work with 2.1
- Rename macOS runtime to `osx-x64` as the old build logic expects 10.12 and breaks running on 10.13 system.
- Remove `PackageReference` to `System.Memory` as it's part of dotnetcore 2.1
- Update search for `crossgen` executable to find the matching version
* Test Update
- Update test tools `WebListener` to latest `asp.net core`
- Marked `AuthHeader Redirect` tests as `Pending` due to change in CoreFX
Extract information about the release tag, number of commits since the tag and the hash of the latest commit within a MSBuild target, and bake that information into version properties of the assemblies appropriately.
`AssemblyVersion` and `FileVersion` are now inferred from the `Version` property, which is inferred by `VersionPrefix`. So now both `AssemblyVersion` and `FileVersion` are 6.0.0.0 for each of PowerShell assemblies, and the `ProductVersion` and `InformationalVersion` are 6.0.0.
