[Predictive Back] [Side Sheet] Added updateBackProgress() predictive back support for coplanar side sheets.

Before this change, coplanar sheets responded to the sheet during finishBackProgress(), in handleBackInvoked(). After this change, coplanar sheets respond to the back progress while the predictive back event is in progress, in updateBackProgress().

PiperOrigin-RevId: 528470353

Author: afohrman

lib/java/com/google/android/material/sidesheet/SideSheetBehavior.java

@@ -991,6 +991,31 @@ public void updateBackProgress(@NonNull BackEvent backEvent) {
       return;
     }
     sideContainerBackHelper.updateBackProgress(backEvent, getGravityFromSheetEdge());
+
+    updateCoplanarSiblingBackProgress();
+  }
+
+  private void updateCoplanarSiblingBackProgress() {
+    if (viewRef == null || viewRef.get() == null) {
+      return;
+    }
+    View sheet = viewRef.get();
+
+    View coplanarSiblingView = getCoplanarSiblingView();
+    if (coplanarSiblingView == null) {
+      return;
+    }
+
+    MarginLayoutParams coplanarSiblingLayoutParams =
+        (MarginLayoutParams) coplanarSiblingView.getLayoutParams();
+    if (coplanarSiblingLayoutParams == null) {
+      return;
+    }
+
+    int updatedCoplanarSiblingAdjacentMargin = (int) (childWidth * sheet.getScaleX() + innerMargin);
+    sheetDelegate.updateCoplanarSiblingAdjacentMargin(
+        coplanarSiblingLayoutParams, updatedCoplanarSiblingAdjacentMargin);
+    coplanarSiblingView.requestLayout();
   }
 
   @Override