Rework/redesign message replies (#9049)

Hello! This PR proposes a redesigned replying system in Zeds chat panel,
inspired by chat applications like [Slack](https://slack.com) and
[Discord](https://discord.com). Feedback and suggestions are welcome! 😄

### TODOs

- [x] Handle replies to removed messages
- [x] Add replied user's profile picture to reply indicator
- [x] Highlight the message that's been selected for replying

--------

### Current Status


https://github.com/zed-industries/zed/assets/146845123/4ed2c2d7-a586-48bd-973c-0d3f033e2c6b

--------

Release Notes:

- Redesigned message replies in the chat panel

---------

Co-authored-by: Thorsten Ball <mrnugget@gmail.com>

crates/ui/src/components/icon.rs

@@ -101,7 +101,8 @@ pub enum IconName {
     ReplaceAll,
     ReplaceNext,
     Return,
-    ReplyArrow,
+    ReplyArrowRight,
+    ReplyArrowLeft,
     Screen,
     SelectAll,
     Shift,
@@ -195,7 +196,8 @@ impl IconName {
             IconName::ReplaceAll => "icons/replace_all.svg",
             IconName::ReplaceNext => "icons/replace_next.svg",
             IconName::Return => "icons/return.svg",
-            IconName::ReplyArrow => "icons/reply_arrow.svg",
+            IconName::ReplyArrowRight => "icons/reply_arrow_right.svg",
+            IconName::ReplyArrowLeft => "icons/reply_arrow_left.svg",
             IconName::Screen => "icons/desktop.svg",
             IconName::SelectAll => "icons/select_all.svg",
             IconName::Shift => "icons/shift.svg",