Use LangVersion preview for all projects

build/SharedVersion.props

@@ -8,7 +8,7 @@
     <RepositoryUrl>https://github.com/AvaloniaUI/Avalonia/</RepositoryUrl>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <NoWarn>CS1591</NoWarn>
-    <LangVersion>latest</LangVersion>
+    <LangVersion>preview</LangVersion>
     <PackageLicenseExpression>MIT</PackageLicenseExpression>
     <PackageIcon>Icon.png</PackageIcon>
     <PackageDescription>Avalonia is a cross-platform UI framework for .NET providing a flexible styling system and supporting a wide range of Operating Systems such as Windows, Linux, macOS and with experimental support for Android, iOS and WebAssembly.</PackageDescription>

src/Markup/Avalonia.Markup.Xaml.Loader/Avalonia.Markup.Xaml.Loader.csproj

@@ -5,7 +5,6 @@
     <IsPackable>true</IsPackable>
     <PackageId>Avalonia.Markup.Xaml.Loader</PackageId>
     <DefineConstants>$(DefineConstants);XAMLX_INTERNAL</DefineConstants>
-    <LangVersion>11</LangVersion>
   </PropertyGroup>
   <!--Disable Net Perf. analyzer for submodule to avoid commit issue -->
   <PropertyGroup>

src/Markup/Avalonia.Markup/Avalonia.Markup.csproj

@@ -2,7 +2,6 @@
   <PropertyGroup>
     <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <RootNamespace>Avalonia</RootNamespace>
-    <LangVersion>11</LangVersion>
   </PropertyGroup>
   <ItemGroup>
     <None Remove="Markup\Parsers\Nodes\ExpressionGrammer" />