Add top-level commands to Dafny and redesign the CLI UI V2

Source/DafnyCore/DafnyConsolePrinter.cs

@@ -52,7 +52,7 @@ public override void ReportBplError(Boogie.IToken tok, string message, bool erro
     realigned_tok.val = tok.val;
     realigned_tok.filename = tok.filename;
     base.ReportBplError(realigned_tok, message, error, tw, category);
-    if (DafnyOptions.O.ShowSnippets) {
+    if (ShowSnippetsOption.Instance.Get(DafnyOptions.O)) {
       WriteSourceCodeSnippet(tok, tw);
     }
 

Source/DafnyCore/DafnyCore.csproj

@@ -19,12 +19,15 @@
     <DefineConstants>TRACE</DefineConstants>
     <TargetFramework>net6.0</TargetFramework>
     <PackageLicenseExpression>MIT</PackageLicenseExpression>
+
+    <NoWarn>$(NoWarn);NU5104</NoWarn> <!-- Required because System.CommandLine is in beta. -->
     <IsPackable>true</IsPackable>
   </PropertyGroup>
-
+  
   <ItemGroup>
       <PackageReference Include="JetBrains.Annotations" Version="2021.1.0" />
       <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.7.0" />
+      <PackageReference Include="System.CommandLine" Version="2.0.0-beta4.22272.1" />
       <PackageReference Include="System.Runtime.Numerics" Version="4.3.0" />
       <PackageReference Include="System.Collections.Immutable" Version="1.7.0" />
       <PackageReference Include="Boogie.ExecutionEngine" Version="2.15.7" />