Fix an issue with posts shown embedded in the notifications popover

[kean]

Fixes #23883. New behavior on iPad:

Simulator.Screen.Recording.-.iPad.Pro.11-inch.M4.-.2024-12-12.at.09.51.42.mp4

Reader will now also no longer lose the current navigation state when opening a deep link with a post.

To test:

Regression Notes

1. Potential unintended areas of impact

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

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

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:

• 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
⚠️	This PR is assigned to the milestone 25.6. The due date for this milestone has already passed. Please assign it to a milestone with a later deadline or check whether the release for this milestone has already been finished.

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[crazytonyli]

This seems to be a roundabout way to check if the notifications view controller is displayed in a popover.

Maybe it's more intuitive to check whether self.modalPresentationStyle or self.navigationController.modalPresentationStyle is popover?

[kean]

Yes, but after a quick search I couldn't find a reliable way to check if something is displayed in a popover. I guess the modalPresentationStyle check could work in this case. I'm a bit reluctant to use it because it's only not a completely reliable indicator as on iPhone .popover is displayed in a sheet by default (obviously not the case here for this screen).

Btw, I'll try to remove isSidebarModeEnabled as well during these couple of weeks. It was added there as a temporary measure during the iPad rework and is a type of a feature flag.