Fix VirtualizedList usage of potentially stale state on cell focus

Summary:
State updates can be batched together idependent of `this.state`, so we should do any calculation deriving state from state within a `setState()` callback. This fixes a bug where we were relying on potentially stale state, a RenderMask derived from `this.state` instead of the `state` callback parameter, when triggering updates from focus.

Note that this is not exercised on Android/iOS, but it on desktop/web. I noticed this a while back while making another change, but that change got abandoned, so this is the independent fix.

Changelog:
[General][Fixed] - Calculate VirtualizedList render mask for focused cell during batched state updates

Reviewed By: javache

Differential Revision: D43073415

fbshipit-source-id: dee4197ec925a6d8d427b63fb063aa4e3b58c595

Author: NickGerleman

packages/virtualized-lists/Lists/VirtualizedList.js

@@ -1229,18 +1229,7 @@ class VirtualizedList extends StateSafePureComponent<Props, State> {
 
   _onCellFocusCapture(cellKey: string) {
     this._lastFocusedCellKey = cellKey;
-    const renderMask = VirtualizedList._createRenderMask(
-      this.props,
-      this.state.cellsAroundViewport,
-      this._getNonViewportRenderRegions(this.props),
-    );
-
-    this.setState(state => {
-      if (!renderMask.equals(state.renderMask)) {
-        return {renderMask};
-      }
-      return null;
-    });
+    this._updateCellsToRender();
   }
 
   _onCellUnmount = (cellKey: string) => {