Folder updates.

- 3 item folder preview has the first item on top of the other 2
- Skip first frame of the folder open animation as there is no
  visual change in that first frame.

Bug: 175329686
Test: visual
Change-Id: Ida9a55ee5093c49f230cdf22d7943b2a6a7ed42d

src/com/android/launcher3/folder/ClippedFolderIconLayoutRule.java

@@ -97,7 +97,7 @@ public class ClippedFolderIconLayoutRule {
 
         double thetaShift = 0;
         if (curNumItems == 3) {
-            thetaShift = Math.PI / 6;
+            thetaShift = Math.PI / 2;
         } else if (curNumItems == 4) {
             thetaShift = Math.PI / 4;
         }