Fix regression of VirtualizedList jumpy header (facebook#22025)

Summary:
Fixes facebook#20956, facebook#21361, facebook#21198, facebook#21468
Keeps the intended outcome of facebook#18105
Pull Request resolved: facebook#22025

Differential Revision: D13941915

Pulled By: cpojer

fbshipit-source-id: 59a0a834ea2d0dd4678e80a82ddaf95cecf87d38

Libraries/Lists/VirtualizedList.js

@@ -806,7 +806,10 @@ class VirtualizedList extends React.PureComponent<Props, State> {
             if (stickyIndicesFromProps.has(ii + stickyOffset)) {
               const initBlock = this._getFrameMetricsApprox(lastInitialIndex);
               const stickyBlock = this._getFrameMetricsApprox(ii);
-              const leadSpace = stickyBlock.offset - initBlock.offset;
+              const leadSpace =
+                stickyBlock.offset -
+                initBlock.offset -
+                (this.props.initialScrollIndex ? 0 : initBlock.length);
               cells.push(
                 <View key="$sticky_lead" style={{[spacerKey]: leadSpace}} />,
               );