Posts & Pages: Refactor table handler #1

[kean]

Some ground work:

• Fix table section header size
• Remove windowless cell (should be no need for it)
• Remove ghosts
• Remove estimated row height
• Fix separator insets in post cells
• Fix post cell background color
• Use standard footer view

Regression Notes

1. Potential unintended areas of impact: Posts & Pages
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.

UI Changes testing checklist:

• 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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📲 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	pr21874-c00b68b
	Version	23.4
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	Commit	c00b68b
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[momo-ozawa]

We actually need to set the root view's backgroundColor to .systemBackground here. The default background color isn't what we want for dark mode.

[kean]

The screen had a .grouped table view style, hence the different background color. Changing it to .plain.