Global lang version

Author: alex-kulakov

Directory.Build.props

@@ -38,6 +38,7 @@
     <NoLogo>true</NoLogo>
     <SuppressNETCoreSdkPreviewMessage>true</SuppressNETCoreSdkPreviewMessage>
     <TargetFramework>netcoreapp3.1</TargetFramework>
+    <LangVersion>9.0</LangVersion>
     <SolutionDir Condition="$(SolutionDir) == ''">$([MSBuild]::EnsureTrailingSlash(
       $([MSBuild]::GetDirectoryNameOfFileAbove('$(MSBuildThisFileDirectory)', 'Orm.sln'))))</SolutionDir>
     <Configuration Condition="$(Configuration) == ''">Debug</Configuration>

Orm/Xtensive.Orm/Xtensive.Orm.csproj

@@ -14,7 +14,6 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <WarningLevel>4</WarningLevel>
     <NoWarn>1591</NoWarn>
-    <LangVersion>9.0</LangVersion>
   </PropertyGroup>
   <PropertyGroup Label="Debug" Condition="'$(Configuration)'=='Debug'">
     <DefineConstants>TRACE;DEBUG</DefineConstants>