BindingsGenerator: Handle global interfaces without named properties

DedicatedWorkerGlobalScope is an object with a Global extended
attribute, but does not define any named property getters. This needs to
be handled by setting the prototype chain to:

    DedicatedWorkerGlobalScope
    ^ DedicatedWorkerGlobalScopePrototype
    ^ WorkerGlobalScopePrototype

(This is different from something like Window, where there is an
intermediate WindowProperties object for named properties.)

Previously, we treated the GlobalMixin object as if it was a simple
prototype object, accidentally setting DedicatedWorkerGlobalScope's
prototype to WorkerGlobalScopePrototype. This caused the expression

    self instanceof DedicatedWorkerGlobalScope

to return false inside workers.

This makes us pass many more of the "/xhr/idlharness.any.worker" WPT
tests than before, rather than failing early.

Tests/LibWeb/Text/input/HTML/DedicatedWorkerGlobalScope-instanceof-worker.js

@@ -0,0 +1,5 @@
+onmessage = function (event) {
+    if (event.data === "run") {
+        postMessage({ result: self instanceof DedicatedWorkerGlobalScope });
+    }
+};