fixes #6354: Sample and Hold for LFO Controller (#6850)

* fixes #6354: Sample and Hold for LFO Controller

LFO controller's "white noise" wave shape didn't respect the frequency knob at all, so
Sample-and-Hold was added to extend the functionality of the LFO Controller with this
random waveshape. The original functionallity can still be accessed by setting the
FREQ knob to minimum (0.01)

---------

Co-authored-by: Kevin Zander <veratil@gmail.com>
Co-authored-by: saker <sakertooth@gmail.com>

include/DataFile.h

@@ -126,6 +126,7 @@ private:
 	void upgrade_defaultTripleOscillatorHQ();
 	void upgrade_mixerRename();
 	void upgrade_bbTcoRename();
+	void upgrade_sampleAndHold();
 
 	// List of all upgrade methods
 	static const std::vector<UpgradeMethod> UPGRADE_METHODS;

include/LfoController.h

@@ -86,6 +86,7 @@ protected:
 	sample_t (*m_sampleFunction)( const float );
 
 private:
+	float m_heldSample;
 	SampleBuffer * m_userDefSampleBuffer;
 
 protected slots: