Implements reliable auto-expand and auto-scroll behavior for the Actions
logs view.
* Expands running or unfinished steps automatically.
* Smoothly scrolls to the latest log line during execution.
* Controlled via existing “Always auto-scroll” and “Expand running
steps” options.
Fixes#35570.
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Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>