AU Client: Prevent parameter change messages being sent during state restoration

This is intended to fix two issues:
- In REAPER, setting automation recording to 'Latch', recording some
  automation, saving and reloading the project, then starting playback causes
  automation data to be overwritten. This appears to be because REAPER
  interprets parameter change messages sent during state restoration as
  originating from the user.
- In Ableton Live, automation lanes are sometimes disabled when loading
  projects. This also seems to be because the setStateInformation call
  may send parameter change messages back to the host.

According to the docs for kAudioUnitProperty_ClassInfo, the host is
required to notify all parameter listeners that the parameter values may
have changed, implying that the plugin need not send its own parameter
change notifications during state restoration.

modules/juce_audio_plugin_client/AU/juce_AU_Wrapper.mm

@@ -724,6 +724,8 @@ public:
 
     ComponentResult RestoreState (CFPropertyListRef inData) override
     {
+        const ScopedValueSetter<bool> scope { restoringState, true };
+
         {
             // Remove the data entry from the state to prevent the superclass loading the parameters
             CFUniquePtr<CFMutableDictionaryRef> copyWithoutData (CFDictionaryCreateMutableCopy (nullptr, 0, (CFDictionaryRef) inData));
@@ -1151,6 +1153,9 @@ public:
 
     void sendAUEvent (const AudioUnitEventType type, const int juceParamIndex)
     {
+        if (restoringState)
+            return;
+
         auEvent.mEventType = type;
         auEvent.mArgument.mParameter.mParameterID = getAUParameterIDForIndex (juceParamIndex);
         AUEventListenerNotify (nullptr, nullptr, &auEvent);
@@ -1186,7 +1191,8 @@ public:
     // this will only ever be called by the bypass parameter
     void parameterValueChanged (int, float) override
     {
-        PropertyChanged (kAudioUnitProperty_BypassEffect, kAudioUnitScope_Global, 0);
+        if (! restoringState)
+            PropertyChanged (kAudioUnitProperty_BypassEffect, kAudioUnitScope_Global, 0);
     }
 
     void parameterGestureChanged (int, bool) override {}
@@ -1811,7 +1817,7 @@ private:
     //==============================================================================
     AudioUnitHelpers::CoreAudioBufferList audioBuffer;
     MidiBuffer midiEvents, incomingEvents;
-    bool prepared = false, isBypassed = false;
+    bool prepared = false, isBypassed = false, restoringState = false;
 
     //==============================================================================
    #if JUCE_FORCE_USE_LEGACY_PARAM_IDS