Add new ma_device_notification_type_unlocked notification

Unlocked notification fires on emscripten upon successful resume of
audio context attached to a device.  This occurs only once per device
and it happens after the browser has received the input event
necessary to begin playing audio on most webpages.  This is due
to autoplay rules.

It is recommended to wait until this event is fired to start a
'main game loop' on the web.

extras/miniaudio_split/miniaudio.c

@@ -7245,6 +7245,14 @@ static void ma_device__on_notification_rerouted(ma_device* pDevice)
 }
 #endif
 
+#if defined(MA_EMSCRIPTEN)
+EMSCRIPTEN_KEEPALIVE
+void ma_device__on_notification_unlocked(ma_device* pDevice)
+{
+    ma_device__on_notification(ma_device_notification_init(pDevice, ma_device_notification_type_unlocked));
+}
+#endif
+
 
 static void ma_device__on_data_inner(ma_device* pDevice, void* pFramesOut, const void* pFramesIn, ma_uint32 frameCount)
 {
@@ -28377,6 +28385,7 @@ static ma_result ma_device_uninit__webaudio(ma_device* pDevice)
             */
             device.webaudio.close();
             device.webaudio = undefined;
+            device.pDevice = undefined;
         }, pDevice->webaudio.deviceIndex);
     }
     #endif
@@ -28872,6 +28881,8 @@ static ma_result ma_device_init__webaudio(ma_device* pDevice, const ma_device_co
                 device.scriptNode.connect(device.webaudio.destination);
             }
 
+            device.pDevice = pDevice;
+
             return miniaudio.track_device(device);
         }, pConfig->deviceType, channels, sampleRate, periodSizeInFrames, pDevice->webaudio.pIntermediaryBuffer, pDevice);
 
@@ -29044,8 +29055,15 @@ static ma_result ma_context_init__webaudio(ma_context* pContext, const ma_contex
             miniaudio.unlock = function() {
                 for(var i = 0; i < miniaudio.devices.length; ++i) {
                     var device = miniaudio.devices[i];
-                    if (device != null && device.webaudio != null && device.state === 2 /* ma_device_state_started */) {
-                        device.webaudio.resume();
+                    if (device != null &&
+                        device.webaudio != null &&
+                        device.state === window.miniaudio.device_state.started) {
+
+                        device.webaudio.resume().then(() => {
+                                Module._ma_device__on_notification_unlocked(device.pDevice);
+                            },
+                            (error) => {console.error("Failed to resume audiocontext", error);
+                            });
                     }
                 }
                 miniaudio.unlock_event_types.map(function(event_type) {

extras/miniaudio_split/miniaudio.h

@@ -3013,7 +3013,8 @@ typedef enum
     ma_device_notification_type_stopped,
     ma_device_notification_type_rerouted,
     ma_device_notification_type_interruption_began,
-    ma_device_notification_type_interruption_ended
+    ma_device_notification_type_interruption_ended,
+    ma_device_notification_type_unlocked
 } ma_device_notification_type;
 
 typedef struct