Remove argument separator from commands (#5080)

* Remove argument separator from commands

Currently, the argument separator (`--`) is only supported on
`dotnet run`. This PR removes it from other commands to make the help and
usage of these command clearer.

* Adding dotnet run message test

* Responding to PR feedback

src/dotnet/commands/dotnet-restore/Program.cs

@@ -19,7 +19,7 @@ namespace Microsoft.DotNet.Tools.Restore
                 Name = "restore",
                 FullName = LocalizableStrings.AppFullName,
                 Description = LocalizableStrings.AppDescription,
-                AllowArgumentSeparator = true,
+                HandleRemainingArguments = true,
                 ArgumentSeparatorHelpText = HelpMessageStrings.MSBuildAdditionalArgsHelpText
             };