Reader: Restore the native scroll-to-top behavior

[dvdchr]

Refs #22770

With the new Reader design (internal ref: pcdRpT-506-p2), we unknowingly brought two scroll views on screen having both scrollsToTop: true, which breaks the native scroll-to-top behavior when tapping the status bar.

The new scroll view comes from the ReaderNavigationMenu, which is written in SwiftUI. There's no direct access to the scrollsToTop property, so we need traverse the generated views and update the property manually after the component is rendered.

The native scroll-to-top in theory should trigger scrollViewDidScrollToTop(_:). In fact, this method is only triggered when scrolling to top from the status bar, but somehow it's not getting called (you had one job... 😅). So I depended on the existing scrollViewDidScroll method and added a little logic on the ReaderTabView that handles the scroll position calculations.

I thought this would be a one-liner, but it turned out to be a fun little rabbit hole! 🐰 🪄

To test

• Launch the Jetpack app and navigate to the Reader tab.
• Scroll down the stream for a bit.
• Tap on the status bar.
• 🔎 Verify that the stream now scrolls to the top.
• 🔎 Verify that the navigation bar is shown after reaching the top.

Regression Notes

1. Potential unintended areas of impact
   Should be none.

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   Manually tested the changes.

3. What automated tests I added (or what prevented me from doing so)
   N/A.

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding unit tests for my changes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

Testing checklist:
Not applicable

• WordPress.com sites and self-hosted Jetpack sites.
• Portrait and landscape orientations.
• Light and dark modes.
• Fonts: Larger, smaller and bold text.
• High contrast.
• VoiceOver.
• Languages with large words or with letters/accents not frequently used in English.
• Right-to-left languages. (Even if translation isn’t complete, formatting should still respect the right-to-left layout)
• iPhone and iPad.
• Multi-tasking: Split view and Slide over. (iPad)

[dangermattic]

	1 Warning
⚠️	View files have been modified, but no screenshot or video is included in the pull request. Consider adding some for clarity.

Generated by 🚫 Danger

[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress Alpha by scanning the QR code below to install the corresponding build.

	App Name	WordPress Alpha
	Configuration	Release-Alpha
	Build Number	pr22771-5993d7d
	Version	24.4
	Bundle ID	org.wordpress.alpha
	Commit	5993d7d
	App Center Build	WPiOS - One-Offs #9075

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[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack Alpha by scanning the QR code below to install the corresponding build.

	App Name	Jetpack Alpha
	Configuration	Release-Alpha
	Build Number	pr22771-5993d7d
	Version	24.4
	Bundle ID	com.jetpack.alpha
	Commit	5993d7d
	App Center Build	jetpack-installable-builds #8118

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[wargcm]

LGTM!