[tree] fix scroll behavior when selecting or expanding a node

Fixes: #3347
Fixes: #1593

The commit addresses an issue with the update tree-widgets after
performing a manual scroll and selecting a tree node causing a poor user
experience.
The fix modifies the logic of the `forceUpdate` to use `clear` instead
of `clearAll` to clear the cache for only the row that is modified and
not the entire cache.

Signed-off-by: Anas Shahid <muhammad.shahid@ericsson.com>

packages/core/src/browser/tree/tree-widget.tsx

@@ -336,7 +336,12 @@ export class TreeWidget extends ReactWidget implements StatefulWidget {
     protected forceUpdate({ resize }: TreeWidget.ForceUpdateOptions = { resize: true }): void {
         if (this.view && this.view.list) {
             if (resize && this.isVisible) {
-                this.view.cache.clearAll();
+                const rowIndex = this.getScrollToRow();
+                if (rowIndex !== undefined) {
+                    this.view.cache.clear(rowIndex, 0);
+                } else {
+                    this.view.cache.clearAll();
+                }
                 this.view.list.recomputeRowHeights();
             } else {
                 this.view.list.forceUpdateGrid();