Comments: Add the new header component

[dvdchr]

Refs #20568

This implements a new (SwiftUI!) header component for Comment screens. Currently, this is only shown in Reader comments when the feature flag is enabled. Here are some previews:

Before	After

⚠️ Note: The featured image thumbnail is not included yet in this PR. It will be added through a separate PR.

To test

• Launch the app.
• Go to App Settings > Debug and ensure that the Comment Moderation Update flag is toggled on.
• Go to any Reader comments.
• Verify that the new header is shown.

Regression Notes

1. Potential unintended areas of impact
   Should be none. The feature is hidden behind a feature flag.

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.

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	pr20753-df561e2
	Version	22.6
	Bundle ID	com.jetpack.alpha
	Commit	df561e2
	App Center Build	jetpack-installable-builds #5118

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[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	pr20753-df561e2
	Version	22.6
	Bundle ID	org.wordpress.alpha
	Commit	df561e2
	App Center Build	WPiOS - One-Offs #6094

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[kyleaparker]

Looks really good to me. The only change I think we could try is a lighter material :)

[mokagio]

Bumping this to 22.7 because I'm starting the 22.6 code freeze today and this is still a draft.

[wargcm]

I checked:
✅ Light/dark mode
✅ Different accessibility sizes
✅ VoiceOver
✅ RtL language

LGTM!

[kean]

You are hopefully going to be able to remove this (and VisualEffectView) soon. There is a discussion when to merge the deployment target bump.

[dvdchr]

Thanks for the heads up, and looking forward to it! I'll create a follow-up PR to remove them once the version bump PR gets merged.