LibWeb: Add BaseAudioContext::nyquist_frequency helper function

As a convenient shorthand :^)

Userland/Libraries/LibWeb/WebAudio/BaseAudioContext.h

@@ -35,6 +35,9 @@ public:
     double current_time() const { return m_current_time; }
     Bindings::AudioContextState state() const { return m_control_thread_state; }
 
+    // https://webaudio.github.io/web-audio-api/#--nyquist-frequency
+    float nyquist_frequency() const { return m_sample_rate / 2; }
+
     void set_onstatechange(WebIDL::CallbackType*);
     WebIDL::CallbackType* onstatechange();