Converge common msbuild properties and targets (#338)

Converge common msbuild properties and targets (#338)

* Converge common msbuild properties and targets

Moving common msbuild properties and targets into the repo root.

* Consolidate analyzers logic into the repo root

Consolidating msbuild analyzers logic centrally in the repo root and
adding a property switch `EnableAnalyzers` to enable analyzers. We
still need to import the Analyzers.props file unconditionally as
libraries currently doesn't use the PackageReference logic in ref and
src projects and instead uses a depproj to create a props file
dynamically.

* More cleanup to fix CoreLib build