Add notifySampleChanged in dispatch and engine:

This method/variables are for notify sample is changed/altered/added/removed.  can be called together with updateSampleTex for sample update.

multipcm: Fix possible desync with instrument and sample parameter

opl4: Split sample table render and sample data render, Add notifySampleChange for refresh sample parameters

src/engine/dispatch.h

@@ -917,6 +917,11 @@ class DivDispatch {
      */
     virtual void notifyWaveChange(int wave);
 
+    /**
+     * notify sample change.
+     */
+    virtual void notifySampleChange(int sample);
+
     /**
      * notify addition of an instrument.
      */