Reader: Add a footer view for the Reader tags feed

[wargcm]

Fixes #23108

Description

Adds the "More" footer view to the Reader tags feed.

Note: There's an existing issue when navigating to a tag feed from the "Your Tags" feed. This is due to the following chain of events:

1. A reader stream view controller is created with the tag slug
2. A lookup happens and then the readerTopic of the stream view controller gets set
3. The didSet of the readerTopic sets the inUse property on the tag managed object and the context is saved
4. The existing "Your Tags" feed now sees a change to the tag object
5. That tag cell is reloaded

This causes the collection view offset to briefly show at the beginning, and then it'll update back to the end of the content when navigating back to the "Your Tags" feed from the tag feed.

I couldn't find a good way to fix this because it appears the inUse property is currently used. I'll keep attempting to look for a solution.

Screenshots

Light	Dark

Testing

To test:

• Launch Jetpack and login
• Navigate to the "Your Tags" feed
• Scroll to the end of a tag's collection view
• 🔎 Verify the "More" footer view is styled correctly
• Tap on the view
• 🔎 Verify it navigates to that tag's feed

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) N/A

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

• [x] I have completed the Regression Notes.
• [x] I have considered adding unit tests for my changes.
• [x] I have considered adding accessibility improvements for my changes.
• [x] 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)

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	App Name	WordPress Alpha
	Configuration	Release-Alpha
	Build Number	pr23109-0a19acf
	Version	24.7
	Bundle ID	org.wordpress.alpha
	Commit	0a19acf816a4ed7a2a1edd0b6915bdc230fb4389
	App Center Build	WPiOS - One-Offs #9709

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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	pr23109-0a19acf
	Version	24.7
	Bundle ID	com.jetpack.alpha
	Commit	0a19acf816a4ed7a2a1edd0b6915bdc230fb4389
	App Center Build	jetpack-installable-builds #8753

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[wargcm]

Maybe at some point we can rewrite the stream view controller. There's a decent amount of strange behavior from the current one, which is very difficult to fix or track down.

We just need to fetch the tags once every time the stream is loaded or the user initiates a refresh gesture.

We'd still need to handle a user's tags changing, unless navigating back counts as loading. They can open one of the tag posts, then tap on a tag for that post, and follow it.

Thanks for the review!