Auto merge of #97383 - dingxiangfei2009:restore-region-scope-tree-query, r=dingxiangfei2009

Try to cache region_scope_tree as a query

This PR will attempt to restore `region_scope_tree` as a query so that caching works again. It seems that `region_scope_tree` could be re-computed for nested items after all, which could explain the performance regression introduced by #95563.

cc `@Mark-Simulacrum` `@pnkfelix` I will try to trigger a perf run here.