upgrade MSFT.EXT and BCL libraries to 8.0+ (#7460)

* upgrade MSFT.EXT and BCL libraries to 8.0+

time to upgrade to the next set of LTS

* can't use langversion 13.0 without .NET 9

* Added `FSharpVersion` back

Akka.Tests.Shared.Internals needs it in order for our C# `FsCheck` helpers to work

Author: Aaronontheweb

src/Directory.Build.props

@@ -15,7 +15,7 @@
   </PropertyGroup>
   <!-- Set the language version for C# if we're not inside an F# project -->
   <PropertyGroup Condition="'$(MSBuildProjectExtension)' == '.csproj'">
-    <LangVersion>11.0</LangVersion>
+    <LangVersion>12.0</LangVersion>
   </PropertyGroup>
   <PropertyGroup>
     <XunitVersion>2.8.1</XunitVersion>
@@ -38,8 +38,8 @@
     <HoconVersion>2.0.3</HoconVersion>
     <ConfigurationManagerVersion>6.0.1</ConfigurationManagerVersion>
     <MultiNodeAdapterVersion>1.5.25</MultiNodeAdapterVersion>
-    <MicrosoftLibVersion>[6.0.*,)</MicrosoftLibVersion>
-    <MsExtVersion>[6.0.*,)</MsExtVersion>
+    <MicrosoftLibVersion>[8.0.*,)</MicrosoftLibVersion>
+    <MsExtVersion>[8.0.*,)</MsExtVersion>
     <AkkaAnalyzerVersion>0.3.0</AkkaAnalyzerVersion>
     <AkkaPackageTags>akka;actors;actor model;Akka;concurrency</AkkaPackageTags>
   </PropertyGroup>