[MaterialDividerItemDecoration] Fixed divider instant appearing or di…

…sappearing on insertion or removal

Resolves #4014
Resolves #3651

GIT_ORIGIN_REV_ID=d044f541f9928db1d03dea1866e8b8e4c699bf87
PiperOrigin-RevId: 601257154

(cherry picked from commit 1371091)

lib/java/com/google/android/material/divider/MaterialDividerItemDecoration.java

@@ -331,6 +331,8 @@ private void drawForVerticalOrientation(@NonNull Canvas canvas, @NonNull Recycle
         int bottom = tempRect.bottom + Math.round(child.getTranslationY());
         int top = bottom - thickness;
         dividerDrawable.setBounds(left, top, right, bottom);
+        int alpha = Math.round(child.getAlpha() * 255);
+        dividerDrawable.setAlpha(alpha);
         dividerDrawable.draw(canvas);
       }
     }
@@ -375,8 +377,9 @@ private void drawForHorizontalOrientation(@NonNull Canvas canvas, @NonNull Recyc
           right = tempRect.right + translationX;
           left = right - thickness;
         }
-
         dividerDrawable.setBounds(left, top, right, bottom);
+        int alpha = Math.round(child.getAlpha() * 255);
+        dividerDrawable.setAlpha(alpha);
         dividerDrawable.draw(canvas);
       }
     }