Alias-free oscillators (#5826)

Add a band-limited, alias-free wavetable oscillator option to the
`Oscillator` class. Use it by default for Triple Oscillator.

Savefiles which do not have this feature enabled (e.g. old
savefiles) will be loaded without this feature to keep the sound
consistent.

Original author: @curlymorphic.
Fixed: @he29-net.

src/core/SampleBuffer.cpp

@@ -23,6 +23,7 @@
  */
 
 #include "SampleBuffer.h"
+#include "Oscillator.h"
 
 #include <algorithm>
 
@@ -62,6 +63,7 @@
 
 
 SampleBuffer::SampleBuffer() :
+	m_userAntiAliasWaveTable(nullptr),
 	m_audioFile(""),
 	m_origData(nullptr),
 	m_origFrames(0),
@@ -352,6 +354,13 @@ void SampleBuffer::update(bool keepSettings)
 
 	emit sampleUpdated();
 
+	// allocate space for anti-aliased wave table
+	if (m_userAntiAliasWaveTable == nullptr)
+	{
+		m_userAntiAliasWaveTable = std::make_unique<OscillatorConstants::waveform_t>();
+	}
+	Oscillator::generateAntiAliasUserWaveTable(this);
+
 	if (fileLoadError)
 	{
 		QString title = tr("Fail to open file");