Fix an issue with comment scrolling offset

[micahmo]

Pull Request Description

This is a quick fix related to comment scrolling in the new post page. It looks like my change in #1630 inadvertently allowed the comments to be scrolled to the very top of the display, due to the extended SafeArea, which is now partly covered by a Container. This fix adds an offset to animateToItem to account for the status bar.

However, this turned out to be tricky, because as a child widget of SafeArea(top: false), accessing the status bar height with MediaQuery.of(context).padding.top always returns 0. Therefore I had to capture the height outside the SafeArea and pass it in. I also had to remove the offset when the top bar is pinned. Now it works well!

Issue Being Fixed

Issue Number: N/A

Screenshots / Recordings

Before

comment_scroll_before.mp4

After

comment_scroll_after.mp4

Checklist

• If a new package was added, did you ensure it uses an appropriate license and is actively maintained?
• Did you use localized strings (and added appropriate descriptions) where applicable?
• Did you add semanticLabels where applicable for accessibility?

[hjiangsu]

LGTM!