chore(windows): refactor C++ and Delphi shared units into static(?) libraries

```diff
- #include "stdafx.h"
+ #include "pch.h"
```

Because our global C++ classes are not yet in a shared library, we have to do dumb things like this where precompiled headers are inconsistent between projects. Yuck. Another possible groundwork project for 15.0?

_Originally posted by @mcdurdin in https://github.com/keymanapp/keyman/pull/4596#discussion_r587968291_