Implement rich replies

[HarHarLinks]

Describe the bug

This has been long outstanding: #2565, #2448, #174, #1741, #971, and more.

It has been very annoying for a long time, but stayed unadressed.
Now element web - the most common client on desktop devices by far - has reworked it's reply look to truncate messages, leading to this issue: element-hq/element-web#18205 (comment). According to that, android is nonconforming to spec in regards of replies.

Sending and displaying replies on android now urgently needs some revision.

[SpiritCroc]

I added rich replies to SchildiChat, relevant commits:

• SchildiChat@6c4c351
• SchildiChat@a32fc6b
• SchildiChat@15d8a91
• SchildiChat@437d281
• SchildiChat@772ff30
• SchildiChat@bbbefae
• SchildiChat@7a83a44
• SchildiChat@1c33519
• SchildiChat@dd83c16
• SchildiChat@4d04e42

I'm not planning to PR these to Element right now (lack of time and motivation to deal with Element design), and they likely won't apply cleanly on top of Element. But if anybody wants to pick them, get them to work with vanilla Element, and create a PR, I'd happily provide a sign-off!