Add Counts of Replies to Comment Threads

[gmeben]

When encountering a thread of inline or overall comments, there's no explicit indicator for how many replies a thread contains. There's also no explicit indicator for any newly added replies. These deficiencies make it difficult for users to recognize at a glance of new comment activity.

Add a count of how many replies a comment thread contains that's visible before a thread is expanded with the "Show Replies" button.

Review Checklist

• Numeric indicators of replies within threads are visible
• Necessary frontend unit testing has been added

Accessibility Checklist

• No new color contrast issues are introduced
• Added text has a font size of at least 16px
• Added text uses plain language

[gmeben]

Feature Request: https://feedback.pilcrow.dev/posts/8/way-to-denote-an-updated-comment

[sattler9]

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