Upgrade any .NET Framework area to .NET Core 3

[crutkas]

.NET Core 3 upgrade

Update all sections that use .NET to .NET Core 3

.NET Framework 4.7.2

• ColorPicker <- done by Jeremy Sinclair (@snickler)
• MarkdownPreviewHandler <- PreviewPane Porting .NET Core 3.1 #8405
• PreviewHandlerCommon <- PreviewPane Porting .NET Core 3.1 #8405
• SvgPreviewHandler <- PreviewPane Porting .NET Core 3.1 #8405
• SVGThumbnailProvider <- PreviewPane Porting .NET Core 3.1 #8405

Tests

• Microsoft.Interop.Tests <- done by Eriawan Kusumawardhono (@eriawan)
• PreviewPaneUnitTests <- PreviewPane Porting .NET Core 3.1 #8405
• UnitTests-PreviewHandlerCommon <- PreviewPane Porting .NET Core 3.1 #8405
• UnitTests-SvgPreviewHandler <- PreviewPane Porting .NET Core 3.1 #8405
• UnitTests-SvgThumbnailProvider <- PreviewPane Porting .NET Core 3.1 #8405
• PowerToysTests <- done by Rafael Rivera (@riverar) WinAppDriver tests

.NET Standard 2.0

• Managed Common
• Telemetry
• Settings.UI.Library
• PowerLauncher.Telemetry

.NET Core 3.1

• FancyZonesEditor
• Settings.UI.Runner
• Settings.UI.UnitTests
• UnitTest-ColorPicker
• ImageResizerUI
• ImageResizerUITests
• PowerLauncher
• Wox.Infrastructure
• Wox.Plugin
• Wox.Test

UWP

• Settings.UI

Things to include

• ReadyToRun should be timed to verify boost. see blog post
• PublishTrimmed to reduce file size. see blog post

[enricogior]

This issue has a pre-requisite #866

We PR is ready but not merged because of the pending dependency.

[enricogior]

Added the resolved label since on our side this is done.
Added the external label to indicate we are waiting of an external dependency to be available.

[yuyoyuppe]

We might need to revert this guy after the migration.