LibJS: Teach GetVariable bytecode op to deal with global variable cache

This mirrors the behavior of Identifer::to_reference() in the AST
interpreter.

Userland/Libraries/LibJS/Bytecode/Op.cpp

@@ -358,11 +358,16 @@ ThrowCompletionOr<void> GetVariable::execute_impl(Bytecode::Interpreter& interpr
     auto get_reference = [&]() -> ThrowCompletionOr<Reference> {
         auto const& string = interpreter.current_executable().get_identifier(m_identifier);
         if (m_cached_environment_coordinate.has_value()) {
-            auto* environment = vm.running_execution_context().lexical_environment;
-            for (size_t i = 0; i < m_cached_environment_coordinate->hops; ++i)
-                environment = environment->outer_environment();
-            VERIFY(environment);
-            VERIFY(environment->is_declarative_environment());
+            Environment* environment = nullptr;
+            if (m_cached_environment_coordinate->index == EnvironmentCoordinate::global_marker) {
+                environment = &interpreter.vm().current_realm()->global_environment();
+            } else {
+                environment = vm.running_execution_context().lexical_environment;
+                for (size_t i = 0; i < m_cached_environment_coordinate->hops; ++i)
+                    environment = environment->outer_environment();
+                VERIFY(environment);
+                VERIFY(environment->is_declarative_environment());
+            }
             if (!environment->is_permanently_screwed_by_eval()) {
                 return Reference { *environment, string, vm.in_strict_mode(), m_cached_environment_coordinate };
             }