Net Core - AppVeyor run tests and build x86/x64

[campersau]

Part of: #3197

Summary:

• run netcore tests on appveyor
• build x86 and x64 so CefSharp.Common.NETCore gets packaged

Changes:

• adjusted appveyor.yml to run netcore tests and build x86/x64 so all nuget packages can be generated

How Has This Been Tested?
https://ci.appveyor.com/project/campersau/cefsharp/builds/34657294

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Updated documentation

Checklist:

• Tested the code(if applicable)
• Commented my code
• Changed the documentation(if applicable)
• New files have a license disclaimer
• The formatting is consistent with the project (project supports .editorconfig)

[AppVeyorBot]

✅ Build CefSharp 84.4.0-CI3663 completed (commit 9bd57cbc99 by @campersau)

[amaitland]

Great thanks 👍