feat(Quote Replies): Option to reply as a reblog

[marcustyphoon]

Description

Working proof of concept.

This implements the ability for Quote Replies to—rather than creating a new draft post with the quoted reply—create a draft reblog of the target post with the quoted reply.

Remake of #1542, stacked on #1662. Resolves #1414.

This diff is, like. So bad, man. But I guess that's what happens when you implement:

• Click activity notification (old)
• Click activity notification (new/"generic")
• Click activity notification (new/"generic", but reply fetch failed; trigger fallback)
• Click post note (reply to your post)
• Click post note (reply to your comment)
• Click post note (mentions you)

and

• Quote reply as new post
• Quote reply as reblog
• Quote reply as reblog, but the post isn't rebloggable; make a new post
• Quote reply as reblog, but the post cannot be fetched; make a new post

I guess that's 24 test cases. Plus one for "click post note; it's not relevant to you and so there should be no meatball menu item shown", so 25. Good times.

Would you believe that this is after probably a solid workday of trying to factor stuff to be simpler?

Testing steps