WebContent+LibWeb+LibJS: Simplify injection of JS console globals

Instead of creating a new global object and proxying everything through
it, we now evaluate console inputs inside a `with` environment.

This seems to match the behavior of WebKit and Gecko in my basic
testing, and removes the ConsoleGlobalObject which has been a source of
confusion and invalid downcasts.

The globals now live in a class called ConsoleGlobalObjectExtensions
(renamed from ConsoleGlobalObject since it's no longer a global object).

To make this possible, I had to add a way to override the initial
lexical environment when calling JS::Interpreter::run(). This is plumbed
via Web::HTML::ClassicScript::run().

Userland/Libraries/LibWeb/HTML/Scripting/ClassicScript.h

@@ -32,7 +32,7 @@ public:
         No,
         Yes,
     };
-    JS::Completion run(RethrowErrors = RethrowErrors::No);
+    JS::Completion run(RethrowErrors = RethrowErrors::No, JS::GCPtr<JS::Environment> lexical_environment_override = {});
 
     MutedErrors muted_errors() const { return m_muted_errors; }