Remove the Gate knob from effects (#8011)

Major changes:
- Remove Gate knob from effects, effectively hard coding its value to zero
- Replace effect RMS calculations with a more efficient way of detecting silent buffers
- Only perform silent buffer detection when `ProcessStatus::ContinueIfNotQuiet` is returned from a plugin AND auto-quit is enabled

Minor changes:
- Remove gate from presets
- Remove gate from .mmp projects
- Move `Effect::processorCount()` to `LadspaEffect`
- Rename `Effect::checkGate` to `Effect::handleAutoQuit`
- Adjust silence threshold for better compatibility with old RMS calculations
- Remove some unnecessary methods from `Effect`
- Reset quiet buffer count in `stopRunning`
- Use positive name for auto-quit boolean
- Simplify `m_autoQuitEnabled` initialization

plugins/LadspaEffect/LadspaEffect.cpp

@@ -279,7 +279,7 @@ void LadspaEffect::pluginInstantiation()
 
 	// Calculate how many processing units are needed.
 	int effect_channels = manager->getDescription( m_key )->inputChannels;
-	setProcessorCount(DEFAULT_CHANNELS / effect_channels);
+	m_processors = DEFAULT_CHANNELS / effect_channels;
 
 	// get inPlaceBroken property
 	m_inPlaceBroken = manager->isInplaceBroken( m_key );

plugins/LadspaEffect/LadspaEffect.h

@@ -61,6 +61,10 @@ public:
 		return m_portControls;
 	}
 
+	ch_cnt_t processorCount() const
+	{
+		return m_processors;
+	}
 
 private slots:
 	void changeSampleRate();
@@ -87,7 +91,8 @@ private:
 	QVector<multi_proc_t> m_ports;
 	multi_proc_t m_portControls;
 
-} ;
+	ch_cnt_t m_processors = 1;
+};
 
 
 } // namespace lmms