Post Details Comments: add view all comments button to comments table

[ScoutHarris]

Ref: #17511
Depends on: #17546

This displays a View All Comments button in the last row of the Comments table. Tapping it will display the threaded comments view.

Also, the comments table no longer shows separators or row selection.

Notes:

• The design has the button border and label different colors. I'll add this functionality in a follow-up PR.
• There are still empty rows above the button where the Comments will eventually be displayed.

To test:

• Enable the postDetailsComments feature.
• Go to Reader > post > details.
• Verify the View All Comments button is displayed.
• Verify tapping it displays the threaded comments view.

Regression Notes

1. Potential unintended areas of impact
   N/A. WIP.

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

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

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.

[peril-wordpress-mobile]

You can trigger an installable build for these changes by visiting CircleCI here.

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[dvdchr]

LGTM!

[peril-wordpress-mobile]

	Warnings
⚠️	This PR is assigned to a milestone which is closing in less than 4 days Please, make sure to get it merged by then or assign it to a later expiring milestone

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