assistant: Change the quote selection crease icon (#16180)

Felt like this icon was more fitting to the idea of selected text, and looked less like a document.

Release Notes:

- N/A

crates/ui/src/components/icon.rs

@@ -254,6 +254,7 @@ pub enum IconName {
     Tab,
     Terminal,
     TextCursor,
+    TextSelect,
     Trash,
     TriangleRight,
     Undo,
@@ -417,6 +418,7 @@ impl IconName {
             IconName::Tab => "icons/tab.svg",
             IconName::Terminal => "icons/terminal.svg",
             IconName::TextCursor => "icons/text-cursor.svg",
+            IconName::TextSelect => "icons/text_select.svg",
             IconName::Trash => "icons/trash.svg",
             IconName::TriangleRight => "icons/triangle_right.svg",
             IconName::Update => "icons/update.svg",