Show replies in context of their threads (#4871)

* Don't reconstruct threads from separate posts

* Remove post-level dedupe for now

* Change repost dedupe condition to look just at length

* Delete unused isThread

* Delete another isThread field

It is now meaningless because there's nothing special about author threads.

* Narrow down slice item shape so it does not need reply

* Consolidate slice validation criteria in one place

* Show replies in context

* Make fallback marker work

* Remove misleading and now-unused property

It was called rootUri but it was actually the leaf URI. Regardless, it's not used anymore.

* Add by-thread dedupe to non-author feeds

* Add post-level dedupe

* Always count from the start

This is easier to think about.

* Only tuner state need to be untouched on dry run

* Account for threads in reply filtering

* Remove repost deduping

This is already being taken care of by item-level deduping. It's also now wrong and removing too much (since it wasn't filtering for reposts directly).

* Calculate rootUri correctly

* Apply Following settings to all lists

* Don't dedupe intentional reposts by thread

* Show reply parent when ambiguous

* Explicitly remove orphaned replies from following/lists

* Fix thread dedupe to work across pages

* Mark grandparent-blocked as orphaned

* Guard tuner state change by dryRun

* Remove dead code

* Don't dedupe feedgen threads

* Revert "Apply Following settings to all lists"

This reverts commit aff86be6d37b60cc5d0ac38f22c31a4808342cf4.

Let's not do this yet and have a bit more discussion. This is a chunky change already.

* Reason belongs to a slice, not item

* Logically feedContext belongs to the slice

* Update comment to reflect latest behavior

src/view/com/posts/FeedItem.tsx

@@ -345,11 +345,9 @@ let FeedItemInner = ({
             postHref={href}
             onOpenAuthor={onOpenAuthor}
           />
-          {!isThreadChild &&
-            showReplyTo &&
-            (parentAuthor || isParentBlocked) && (
-              <ReplyToLabel blocked={isParentBlocked} profile={parentAuthor} />
-            )}
+          {showReplyTo && (parentAuthor || isParentBlocked) && (
+            <ReplyToLabel blocked={isParentBlocked} profile={parentAuthor} />
+          )}
           <LabelsOnMyPost post={post} />
           <PostContent
             moderation={moderation}