add cutoff and pulse width slides for C64, SID2 and SID3

Also add clipping for ADSR, duty and cutoff when in instrument types you go SID3 -> SID2 or SID2 -> C64 or SID3 -> C64

src/engine/dispatch.h

@@ -279,6 +279,9 @@ enum DivDispatchCmds {
   DIV_CMD_SID3_FILTER_MATRIX,
   DIV_CMD_SID3_FILTER_ENABLE,
 
+  DIV_CMD_C64_PW_SLIDE,
+  DIV_CMD_C64_CUTOFF_SLIDE,
+
   DIV_CMD_MAX
 };