Improve UI of popover buttons when hovering over chat messages (#9041)

### Before


https://github.com/zed-industries/zed/assets/146845123/4a16c1ce-a671-4e39-abc9-3a0cb25bc0cd

### After


https://github.com/zed-industries/zed/assets/146845123/cfab3d00-246e-427d-9c40-8ee520a0a186




Release Notes:
- Improved the UI of popover buttons when hovering over chat messages.

crates/ui/src/components/icon.rs

@@ -101,6 +101,7 @@ pub enum IconName {
     ReplaceAll,
     ReplaceNext,
     Return,
+    ReplyArrow,
     Screen,
     SelectAll,
     Shift,
@@ -194,6 +195,7 @@ 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::Screen => "icons/desktop.svg",
             IconName::SelectAll => "icons/select_all.svg",
             IconName::Shift => "icons/shift.svg",