Support for Modern UWP

[devsko]

This PR adds support for Modern UWP (currently in preview) as described here Modernize your UWP app with preview UWP support for .NET 9 and Native AOT
Build prerequisites

• .NET 9 RC2
• Windows SDK 26100

I also changed how the font files find their way into the APPX because

• in classic UWP they were copied to the root directory and not found during runtime at all
• in modern UWP they were found but also visible in solution explorer

[davidxuang]

Hi,

These changes look good overall, but for the edits about the assets:

• Is there any reference regarding this?
• Should this be adapted to WinUI 3 port as well?

Thanks for your contributions.

[devsko]

Hey @davidxuang

Is there any reference regarding this?

The contentFiles NuGet feature doesn't work reliably for legacy projects like (legacy) UWP. For me it didn't work at all, and I had to hack the copy font files.
In SDK projects like modern UWP or WinUI, they work but are always visible - and editable - in solution explorer.

There are several open issues describing this (i.e. dotnet/project-system#3431).
The NuGet build and buildTransitive assets are described here https://learn.microsoft.com/en-us/nuget/concepts/msbuild-props-and-targets and here https://github.com/NuGet/Home/wiki/Allow-package--authors-to-define-build-assets-transitive-behavior

Should this be adapted to WinUI 3 port as well?

Absolutely, if you want, i can add it to this PR.

[davidxuang]

I've merge the changes about the assets and adapted it to WinUI. For the modern UWP part I will wait for the official release of .NET. Are you sure that net8.0-windows instead of net9.0-windows will work for UWP?

[devsko]

Double checked that it works for TargetFramework net8. You need .net9 rc2 or higher SDK to build though.

[devsko]

I am just merging your changes.
Right now the changes in build\uap10.0.17763.0\FluentIcons.Uwp.props do NOT work in legacy project system. That is part of the bug. In legacy project system, it only works this way:

<Project>

  <ItemGroup Condition="'$(OutputType)' == 'AppContainerExe'">
    <Content Include="$(MSBuildThisFileDirectory)..\..\content-transitive\**\*.*">
      <Link>%(RecursiveDir)%(Filename)%(Extension)</Link>
    </Content>
  </ItemGroup>

</Project>

(In SDK project system this bug is fixed)