The new service extension `getRootWidgetTree` can be used instead of the existing:
* `getRootWidgetSummaryTree` --> use`getRootWidgetTree` with parameters `isSummaryTree=true`
* `getRootWidgetSummaryTreeWithPreviews` --> use `getRootWidgetTree` with parameters `isSummaryTree=true` and `withPreviews=true`
This new service extension will enable Flutter DevTools to combine the widget summary tree with the widget details tree by calling `getRootWidgetTree` with `isSummary=false` and `withPreviews=true`.
Closes https://github.com/flutter/devtools/issues/7894