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/engine.h

@@ -748,6 +748,8 @@ class DivEngine {
     void notifyInsChange(int ins);
     // notify wavetable change
     void notifyWaveChange(int wave);
+    // notify sample change
+    void notifySampleChange(int sample);
 
     // dispatch a command
     int dispatchCmd(DivCommand c);