WinUI 3 support

[fubar-coder]

This tries to fix #31, but is blocked due to microsoft/microsoft-ui-xaml#9959.

This PR contains a fully functional DLL and demo application, which are mostly copies from the WPF implementation.

Differences from the WPF implementation include:

• The Data property returns a Geometry object now

Requirements:

• .NET SDK 8.0.401
• VS 2022 17.11.2

TODO

• Find workaround/fix for Build errors when using "dotnet build" microsoft/microsoft-ui-xaml#9959
• Find workaround for Platform.xml not found microsoft/CsWinRT#1736
• Update build configuration to create a successful build

[SKProCH]

Hello, @fubar-coder

Can you also include a github actions script changes to support auto building library for auto publishing on nuget on icons change?

[fubar-coder]

Adding a EnableMsixTooling property fixes a part of the problems I encountered. The missing Platform.xml might be a bug in CsWinRT (microsoft/CsWinRT#1736).

The build environment needs an installed Win 10 SDK (including the UAP platform stuff), which means that the build must(?) be run under windows, using the - for example - ChristopheLav/windows-sdk-install build action, but I haven't tested it yet.

[SKProCH]

Yep, current build environment is already on windows, since i also need to build WPF library, so probably windows not a problem here. But i also doesn't success while trying to setup CI build under windows, so probably it also should be in scope of this PR.

[fubar-coder]

@SKProCH Can you approve the workflow? It'd help testing the workflow 😀

[fubar-coder]

@SKProCH PR is ready for review

[fubar-coder]

I'd like to lower the required SDK version to 10.0.18362.0, because 10.0.22621.0 seems too high. There are still some Win10 machines out there 😄

[SKProCH]

Feed free to do it, if it would work.

[fubar-coder]

The package requires the SDK version 10.0.18362.0, while the demo application requires 10.0.19041.0, due to its reliance on Rx.NET.

EDIT: The CI should work fine though, because it only builds the icon package, not the demo apps.