Upgrade: Uno to 5.2 and use single Project for Samples

[inforithmics]

I upgraded to Uno 5.2 and use the new single Project Infrastructure for the Sample, All platforms are now in one project like maui.

• WinUI
• Browser
• Android
• iOS

Things done:

1. A lot of Code was removed mainly from the different Uno.WinUI Samples targets
2. Uno.Check runs now in the github actions so that all Uno dependencies are installed.
3. Uno Version is now managed in the global.json

 "msbuild-sdks": {
   "Uno.Sdk": "5.2.95"
 }

5. Skia is referenced with the UnoFeatures

<UnoFeatures>
  Skia;
</UnoFeatures>

4. Removed .NET 7 Target because .NET 7 is end of Life in 2024 May

[pauldendulk]

This is a great improvement. Lots of files removed. I have a few remarks and questions to look at.

[inforithmics]

@pauldendulk I adressed the comments, the "msbuild-sdks": I couldn't move downwards it really needs to be in the global.json file this value is used read by Uno to make make the single project work. It provides the Version Number for all Uno components.

[pauldendulk]

All great. I like all the cleaning up done in the later commits.

[pauldendulk]

This will make the ci/cd faster?

[inforithmics]

Yes but I had to revert it because package with checkin hash needs history. Until the last version tag.