Generating CLI tool usages

Is there a way to get the usages generated to reflect that a program is intended to used as a CLI tool? What I would like to see is the `--help` switch return the following, similar to how `dotnet test` does.

I have tried setting the `RootCommand.Name` property to "dotnet mytool" but that threw an `ArgumentException` about whitespace. I have also looked at using a custom `IHelpBuilder`, but overriding `AddUsage` to add this is looking like a _lot_ of work.

Currently `--help` produces this:
```
C:\Users\Paul>dotnet mytool --help
mytool:
My Tool

Usage:
mytool [options]

Options:
--dry-run Executes the command without making any changes.
-?, -h, --help Show help and usage information
```

What I would like to see is:
```
C:\Users\Paul>dotnet mytool --help
mytool:
My Tool

Usage:
dotnet mytool [options]

Options:
--dry-run Executes the command without making any changes.
-?, -h, --help Show help and usage information
```

Start by tracing how RootCommand.Name is validated and how the default help builder, especially IHelpBuilder.AddUsage, formats the Usage section. Compare the current and requested --help output to determine where a multi-word invocation such as "dotnet mytool" could be represented. Done means the generated usage shows "dotnet mytool [options]" without requiring a custom help builder.

Written by the indexing model from the issue text.