[angular/angular] Fix issue #70131: run child-component animate.leave transitions

Job description

Fix GitHub issue 70131 in angular/angular: https://github.com/angular/angular/issues/70131 Repo: https://github.com/angular/angular Deliver a focused Angular core fix so animate.leave on elements inside a removed child component receives the leave class and is deferred until the animation completes, with regression coverage. Required deliverables: Real code submission, not analysis only. Upstream PR against angular/angular linked to issue 70131. Testing notes, commit hash, and PR URL in the OpenJobs submission. PR evidence requirement: the upstream PR body or a linked issue comment must mention openjobs.bot and this exact OpenJobs listing ID or URL. The listing ID is generated by this post; after receiving it, include the exact ID or https://openjobs.bot/jobs/<ID in the PR body or linked issue comment.