Add an inline "Go to original post to see all replies" message when viewing remote toots

[audiodude]

Pitch

We propose adding an inline hint when viewing a toot that allows the user to be aware of the problem and find all replies easily:

Motivation

Full problem description with bug links and proposed solution here:

https://docs.google.com/document/d/1YpdrZVTrk-yt0GpnSxuDybYvFQOA0B-IfkELBYNwSOg/edit

TLDR:

When a user views a toot today, they are likely to miss some if not most of the replies to the toot. This is especially pronounced for users on smaller instances. The reason for this is that the user’s own server only holds replies to the parent toot from accounts that are followed by someone on that user’s server.

[audiodude]

The following issues have been identified as reporting or referencing this problem:

#14017: can't see toots on people's profiles or replies to many toots from self-hosted instance
#18150: UI button to "see all conversation" using context API
#9409: Fetch whole conversation threads
#34: Backfill statuses from remote accounts when first subscribed
#17213: View older posts from other servers
#3794: [enhancement] Web UI: Some toots are not shown

[shleeable]

I'd rather have a "sync toots" button, to pull in replies on demand.

[audiodude]

I've added a note to the doc copied here for convenience:

It seems that a solution that pulled in the toots directly, a so-called “Server integrated solution” as described below, would be preferable. However, we believe that the UI only approach is a good middle ground to start off with given that it is easily implemented and serves to educate users that the problem even exists.

[gabeklavans]

I think this is a pretty big issue, and a decent solution for now. It's pretty disheartening to know that I'm missing ~30% of all replies when I use mastodon on my relatively mid-large sized instance. I'm sure a "sync" button has a slew of technical challenges itself, so I'd like this change as a stop-gap.