LibWebView: Handle mutliple audio tracks when audio play state changes

For example, if a page has multiple audio elements all actively playing
audio, we don't want to broadcast a play state change when only one of
them stop playing.

Userland/Libraries/LibWebView/ViewImplementation.h

@@ -260,6 +260,7 @@ protected:
     RefPtr<Core::Promise<LexicalPath>> m_pending_screenshot;
 
     Web::HTML::AudioPlayState m_audio_play_state { Web::HTML::AudioPlayState::Paused };
+    size_t m_number_of_elements_playing_audio { 0 };
 };
 
 }