LibWeb: Start filling out BaseAudioContext/AudioContext interfaces

- Fills out both IDLs and implements some basic attributes/methods.
- No actual audio processing yet though :^)

Userland/Libraries/LibWeb/WebAudio/BaseAudioContext.cpp

@@ -5,6 +5,7 @@
  */
 
 #include <LibWeb/Bindings/Intrinsics.h>
+#include <LibWeb/HTML/EventNames.h>
 #include <LibWeb/WebAudio/BaseAudioContext.h>
 
 namespace Web::WebAudio {
@@ -24,4 +25,14 @@ JS::ThrowCompletionOr<void> BaseAudioContext::initialize(JS::Realm& realm)
     return {};
 }
 
+void BaseAudioContext::set_onstatechange(WebIDL::CallbackType* event_handler)
+{
+    set_event_handler_attribute(HTML::EventNames::statechange, event_handler);
+}
+
+WebIDL::CallbackType* BaseAudioContext::onstatechange()
+{
+    return event_handler_attribute(HTML::EventNames::statechange);
+}
+
 }