set v12 unconditionally and globally

Author: antonfirsov

Directory.Build.props

@@ -21,9 +21,9 @@
   <!-- Import the shared global .props file -->
   <Import Project="$(MSBuildThisFileDirectory)shared-infrastructure\msbuild\props\SixLabors.Global.props" />
 
-  <PropertyGroup Condition="$(SIXLABORS_TESTING_PREVIEW) == true">
+  <PropertyGroup>
     <!-- Workaround various issues bound to implicit language features. -->
-    <LangVersion>preview</LangVersion>
+    <LangVersion>12.0</LangVersion>
   </PropertyGroup>
 
   <!--

src/ImageSharp/ImageSharp.csproj

@@ -13,7 +13,6 @@
     <PackageTags>Image Resize Crop Gif Jpg Jpeg Bitmap Pbm Png Tga Tiff WebP NetCore</PackageTags>
     <Description>A new, fully featured, fully managed, cross-platform, 2D graphics API for .NET</Description>
     <Configurations>Debug;Release</Configurations>
-    <LangVersion>12.0</LangVersion>
   </PropertyGroup>
 
   <!--  This enables the nullable analysis and treats all nullable warnings as error-->

tests/ImageSharp.Benchmarks/ImageSharp.Benchmarks.csproj

@@ -12,7 +12,6 @@
     <Configurations>Debug;Release</Configurations>
     <!-- Uncomment this to run benchmarks depending on Colorful or Pfim (colorspaces and TGA): -->
     <!--<SignAssembly>false</SignAssembly>-->
-    <LangVersion>12.0</LangVersion>
   </PropertyGroup>
 
   <PropertyGroup>

tests/ImageSharp.Tests.ProfilingSandbox/ImageSharp.Tests.ProfilingSandbox.csproj

@@ -14,7 +14,6 @@
     <EnsureNETCoreAppRuntime>false</EnsureNETCoreAppRuntime>
     <Configurations>Debug;Release</Configurations>
     <ValidateExecutableReferencesMatchSelfContained>false</ValidateExecutableReferencesMatchSelfContained>
-    <LangVersion>12.0</LangVersion>
   </PropertyGroup>
 
   <Choose>

tests/ImageSharp.Tests/ImageSharp.Tests.csproj

@@ -7,7 +7,6 @@
     <Platforms>AnyCPU;x64;x86;ARM64</Platforms>
     <RootNamespace>SixLabors.ImageSharp.Tests</RootNamespace>
     <Configurations>Debug;Release</Configurations>
-    <LangVersion>12.0</LangVersion>
   </PropertyGroup>
 
   <Choose>