…ms array handling (pythonnet#1163)

…ad resolution

…cedence

Bad params object[] precedence

* Add Python 3.9 to CI
* Update AppVeyor image and always install all requirements
* Add Python 3.9 interop file
* Fix geninterop script and regenerate interop39.cs
    - Only record structs when they are defined, not when they are declared
    - If a struct was only declared when a typedef was created, it won't
      contain its member declarations. Those have to be drawn from the
      recorded structs instead.
   - Rename internal members of AstParser to make it easier to debug

…et#1375)

This occured in trying to use F# code from Python. As the `.Name` property
returns `null`, `ContainsKey` fails.

Related documentation:
https://docs.microsoft.com/en-us/dotnet/api/system.reflection.parameterinfo.name