Grant read access to osmd and cursor member elements (#452)

part of #448

src/OpenSheetMusicDisplay/Cursor.ts

@@ -159,4 +159,12 @@ export class Cursor {
     // Set the actual image
     this.cursorElement.src = c.toDataURL("image/png");
   }
+
+  public get Iterator(): MusicPartManagerIterator {
+    return this.iterator;
+  }
+
+  public get Hidden(): boolean {
+    return this.hidden;
+  }
 }

src/OpenSheetMusicDisplay/OpenSheetMusicDisplay.ts

@@ -481,5 +481,18 @@ export class OpenSheetMusicDisplay {
     public set AutoResizeEnabled(value: boolean) {
         this.autoResizeEnabled = value;
     }
+
+    public get Sheet(): MusicSheet {
+        return this.sheet;
+    }
+    public get Drawer(): VexFlowMusicSheetDrawer {
+        return this.drawer;
+    }
+    public get GraphicSheet(): GraphicalMusicSheet {
+        return this.graphic;
+    }
+    public get DrawingParameters(): DrawingParameters {
+        return this.drawingParameters;
+    }
     //#endregion
 }