* Add .NET 8 target to packable projects
* Update test projects
* Update sample projects to target .NET 8
* Update main Avalonia package to target .NET 8 as well
* Remove MSBuildEnableWorkloadResolver hack and some minor change
* Use net8.0 in nuke build as well
* Pin 8.0.0 SDK
* Adjust API validation
* Pin a valid version
* Remove net461 target from Avalonia package
* Remove unused net6.0 target from Avalonia.Designer.HostApp
* Adjust API diff
* Update ControlCatalog.Android.csproj
* Remove MSBuildEnableWorkloadResolver
* Fix Browser issues on .NET 8
* Fix .NET 8 error
* Fix merge conflicts
* Replace explicit TFMs in .csproj files with a centralized registry
* Fix merge conflict
* Fix AvsLegacyWindowsTargetFrameworks and add hacks for the tests
* Update XCode project CommandLineArgument
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Co-authored-by: Nikita Tsukanov <keks9n@gmail.com>
This was signalled for removal in #9553, but I was hesitant to do it because it will be in use by a lot of code in order to override `StyleKey`. Instead of removing it, deprecate it and provide a virtual `StyledElement.StyleKeyOverride` property as the supported way of overriding a control's style key.
The Nullable annotations on netstandard2.0 are incomplete and incorrect in places. Ignore nullable warnings on netstandard2.0 and make them errors on later target frameworks.