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.

include/DataFile.h

@@ -121,6 +121,7 @@ private:
 	void upgrade_noHiddenClipNames();
 	void upgrade_automationNodes();
 	void upgrade_extendedNoteRange();
+	void upgrade_defaultTripleOscillatorHQ();
 
 	// List of all upgrade methods
 	static const std::vector<UpgradeMethod> UPGRADE_METHODS;