Synchronized fixed

…finalizer

…finalizer

- Use `BorrowedReference` where applicable
- Readd `OperatingSystemName` and `MachineName` for now

…thonnet#930)

This addresses the following scenario:

1. A C# object `a` is created and filled with some data.
2. `a` is passed via Python.NET to Python. To do that Python.NET
   creates a wrapper object `w`, and stores reference to `a` in one of
   its fields.
3. Python code later passes `w` back to C#, e.g. calls `SomeCSharpMethod(w)`.
4. Python.NET has to unwrap `w`, so it reads the reference to `a` from it.

Prior to this change in 4. Python.NET had to determine what kind of an
object `a` is. If it is an exception, a different offset needed to be
used. That check was very expensive (up to 4 calls into Python
interpreter).

This change replaces that check with computing offset unconditionally
by subtracting a constant from the object size (which is read from the wrapper),
thus avoiding calls to Python interpreter.

Co-authored-by: Victor Milovanov <lost@losttech.software>

Add a check to see if the last parameter is a params parameter. Set the correct flag to show that it is a paramsArray function.

Fixes pythonnet#943 and pythonnet#331.

- Add .NET Foundation
- Remove Python 3.8.0 warning

…honnet#1147)

…ms array handling (pythonnet#1163)

Drop Python 2 support

…ythonnet#1170)