Omit `#class` for simple values

[amomchilov]

Fixes Ruby/vscode-rdbg#37

This PR depends on the changes in https://github.com/ruby/debug/pull/1001. Only this last commit of this PR is unique to this change.

Description

The class of many values is self-evident and just clutters the UI:

Before	After

(false and nil don't have it, because of this bug described here)

This PR omits the usual #class member for instances of these classes:

• NilClass
• FalseClass
• TrueClass
• Symbol
• String
• Integer
• Float
• Class
• Module
• Array
• Hash

The result is a much tidier UI you see in the "After" screenshot above.

This change still keeps the #class for other types, including subclasses of these simple types. For example, HashWithIndifferentAccess is a subclass of Hash. For clarity, we preserve its #class, but omit it for regular hashes.

[ko1]

Class and Module is not clear with the names so I want to leave them.