Right align scrollToIndex in RTL

Summary:
This fixes up behavior on Android so that `scrollToIndex` aligns the right edge of the cell of the given index to the right edge of the scrollview viewport. We do not incorporate RTL on iOS which inverts x/y coordinates from scroller (but not layout).

Changelog:
[General][Fixed] - Right align scrollToIndex in RTL

Differential Revision: D47978637

fbshipit-source-id: 4548098b755d40102a5442bed81deef94a8e39d6

packages/virtualized-lists/Lists/VirtualizedList.js

@@ -1492,24 +1492,24 @@ class VirtualizedList extends StateSafePureComponent<Props, State> {
       ...
     }>,
   ): number {
-    let offset = this._selectOffset(metrics);
-
     const {horizontal, rtl} = this._orientation();
-    if (horizontal && rtl && Platform.OS !== 'ios') {
-      offset = this._selectLength(contentSize) - offset;
+    if (Platform.OS === 'ios' || !(horizontal && rtl)) {
+      return this._selectOffset(metrics);
     }
 
-    return offset;
+    return this._selectLength(contentSize) - this._selectOffset(metrics);
   }
 
   _cartesianScrollOffset(offset: number): {x?: number, y?: number} {
     const {horizontal, rtl} = this._orientation();
-    const normalizedOffset =
-      horizontal && rtl && Platform.OS !== 'ios'
-        ? this._listMetrics.getContentLength() - offset
-        : offset;
+    if (Platform.OS === 'ios' || !(horizontal && rtl)) {
+      return horizontal ? {x: offset} : {y: offset};
+    }
 
-    const cartOffset = this._listMetrics.cartesianOffset(normalizedOffset);
+    // Add the visible length of the scrollview so that the offset is right-aligned
+    const cartOffset = this._listMetrics.cartesianOffset(
+      offset + this._scrollMetrics.visibleLength,
+    );
     return horizontal ? {x: cartOffset} : {y: cartOffset};
   }