Ability to edit local echos again.

### Steps to reproduce

1. Send a message with a typo
2. Try to edit it by hitting the up arrow key
3. Discover yourself editing the wrong message
4. Press up/down until the app lets you actually edit the message you just sent.

### Outcome

#### What did you expect?

One of the things that Element has supported since we first implemented edits was the ability to edit local echos, which is a surprisingly common for making quick fixes to messages immediately after you send them. On Element X we bent over backwards to support it in rust-sdk; on js-sdk we've had it since bruno first implemented it back in 2019: https://github.com/matrix-org/matrix-js-sdk/pull/920.

This is the sort of more refined feature which makes the difference between a proper collaboration app like Element and a crap messenger like iMessage (which doesn't have it).

#### What happened instead?

There was some edge case where sometimes EW sent edits which referred to a placeholder event ID which would confused EX, and the whole feature got removed.

Please can we either revert that, or add some workaround to stop it ever sending edits which refer to placeholder event IDs.

### Operating system

_No response_

### Application version

current nightly

### How did you install the app?

_No response_

### Homeserver

_No response_

### Will you send logs?

No