Fix Linux popup and flyout issues.

[danwalmsley]

Fixes #12412

[Whem]

I tested on Debian 12 and its works as well, but its only works if I change the Nuget.Config file :

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <add key="nuget" value="https://api.nuget.org/v3/index.json" />
    <add key="avalonia-all" value="https://nuget-feed-all.avaloniaui.net/v3/index.json" />
  </packageSources>
  <packageSourceMapping>
    <packageSource key="avalonia-all">
      <package pattern="*" />
    </packageSource>
    <packageSource key="nuget">
      <package pattern="*" />
    </packageSource>
  </packageSourceMapping>
</configuration>

[soosr]

@MarnixCroes @Whem Could you guys do a final test? If Flyouts are working

[Whem]

tACK

[MarnixCroes]

it doesn't build, CI also failing

[molnard]

@danwalmsley I was not able to add my commit to this PR. Please fix it.

Steps for the Contributor

• Ensure the "Allow edits from maintainers" checkbox is selected for the PR.
• Check their fork's settings for any restrictions that might prevent maintainers from pushing commits.

[MarnixCroes]

@molnard was this merged on purpose? #12505 would be enough, no?
master is broken now

[molnard]

Thx for noticing. If I merge another PR that is based on this - this will look like merged, however I merged #12506

[molnard]

master is broken now

Hmm then I overlooked something. It is working for me. How is it broken for you @MarnixCroes ?

[MarnixCroes]

running 87f8eef, I got errors like this and failing to start
twice after dotnet run

error NU1301: Failed to retrieve information about 'Avalonia' from remote source 'https://nuget-feed-all.avaloniaui.net/v3/package/avalonia/index.json'.

but now trying again, still running 87f8eef, it's working.
so idk