Refactor conditions for the _UnoResizetizerIsWindowsAppSdk property

[nickrandolph]

Current behavior

As mentioned here there is a test for windows that will result in true for WPF (which probably isn't correct) and the test for ProjectReunion is no longer relevant

Expected behavior

Refactor to address the detection of windows and the removal of projectreunion

How to reproduce it (as minimally and precisely as possible)

Environment

Nuget Package:

Package Version(s):

Affected platform(s):

• iOS
• Android
• WebAssembly
• WebAssembly renders for Xamarin.Forms
• Windows
• Build tasks

Visual Studio:

• 2017 (version: )
• 2019 (version: )
• for Mac (version: )

Relevant plugins:

• Resharper (version: )

Anything else we need to know?