MAX_PATH limitations still impact .NET Core

On .NET Core, the managed file system API have some tricks to support long paths irrespective of the application manifest (and machine configuration).

However, on .NET Core

* MSBuild is hosted by dotnet.exe, which does not opt in to long paths in its manifest
* MSBuild does a lot of file system work by P/Invoking straight to Win32

The fixes here are either:

1. Use the x-plat, portable file system code on .NET Core for Windows as on .NET core for other OSes.
2. Get dotnet.exe manifest changed.

(1) would work for all Windows machines running .NET Core msbuild, so that's my preference but I may not understand all the ramifications of doing that.