* Update mono props: support OSX and more .NET Framework versions

A potential solve for #6180 that uses msbuild built-ins to determine the target OS and pivots off of that to set the FrameworkPathOverride.  I included a `MonoRoot` property to allow for easy integration into the build process that fsharp/fsharp uses, which allows for a 'floating' mono root.

* add osx build jobs matching the linux jobs, and add a matrix entry to build the compiler for .net framework using mono

* don't try to build anything for .net framework on non-windows

this required additional build work that may conflict with upcoming work, so we'll just settle for building the existing components on macos at all in CI