Ability to view edit history.

**Is your feature request related to a problem? Please describe.**

Many apps (Element Web, classic Element iOS/Android, Threema, Signal, even iMessage) let you view the edit history of a given message. This is particularly important for dealing with bad-faith edits (i.e. where someone edited a prior msg to change the meaning of the subsequent conversation).

**Describe the solution you'd like**

Show the diffs of history of messages in the context menu when you long-tap on an edited message.

**Describe alternatives you've considered**

iMessage's UI is quite cute, in that it pops open a thread to show you the history inlined int he timeline. But it's overkill imo; would be good enough just to show the history in the context menu.

**Additional context**

It's frustrating from a competitor-parity perspective that the others have this, and we used to, but we don't any more.