Add slug and excerpt fields to Page Settings

[kean]

Fixes https://github.com/wordpress-mobile/WordPress-iOS/issues/11225

To test:

• Open Page Settings
• ✅ Verify that the settings contain "Slug" and "Excerpt" fields
• Update the fields and save
• ✅ Verify that the changes are reflected on the web

Regression Notes

1. Potential unintended areas of impact: Page Settings
2. What I did to test those areas of impact (or what existing automated tests I relied on): manual
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:

• [ ] 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)

[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	pr23135-15a2476
	Version	24.8
	Bundle ID	org.wordpress.alpha
	Commit	15a2476596a63180b22117c530d4f0eb88512602
	App Center Build	WPiOS - One-Offs #9764

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[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	pr23135-15a2476
	Version	24.8
	Bundle ID	com.jetpack.alpha
	Commit	15a2476596a63180b22117c530d4f0eb88512602
	App Center Build	jetpack-installable-builds #8810

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[kean]

There's a visual bug - some times the "excerpt" label isn't centered vertically

Is there a way to reproduce it? It's likely something to do with the odd layout hacks in WPTableViewCell... should replace this with SwiftUI.