terminal: Send modifier sequences for the delete key

Delete with a modifier produced no input at all. Since the alt handling
was limited to single characters, alt-delete stopped sending the bogus
`ESC delete` and fell through to nothing, because delete was missing from
the modified special keys table next to insert, pageup and pagedown.

Modified delete now goes out as `CSI 3 ; <modifier> ~`, the same
encoding xterm and alacritty use.

Closes #64721

crates/terminal/src/mappings/keys.rs

@@ -199,6 +199,7 @@ pub(crate) fn to_esc_str(
             "f19" => Some(format!("\x1b[33;{}~", modifier_code)),
             "f20" => Some(format!("\x1b[34;{}~", modifier_code)),
             "insert" => Some(format!("\x1b[2;{}~", modifier_code)),
+            "delete" => Some(format!("\x1b[3;{}~", modifier_code)),
             "pageup" => Some(format!("\x1b[5;{}~", modifier_code)),
             "pagedown" => Some(format!("\x1b[6;{}~", modifier_code)),
             "end" => Some(format!("\x1b[1;{}F", modifier_code)),
@@ -369,7 +370,7 @@ mod test {
         let gpui_keys = [
             "up", "down", "right", "left", "f1", "f2", "f3", "f4", "f5", "f6", "f7", "f8", "f9",
             "f10", "f11", "f12", "f13", "f14", "f15", "f16", "f17", "f18", "f19", "f20", "insert",
-            "pageup", "pagedown", "end", "home",
+            "delete", "pageup", "pagedown", "end", "home",
         ];
 
         for key in gpui_keys {
@@ -402,6 +403,28 @@ mod test {
         }
     }
 
+    #[test]
+    fn test_modified_delete() {
+        let cases = [
+            ("delete", "\x1b[3~"),
+            ("shift-delete", "\x1b[3;2~"),
+            ("alt-delete", "\x1b[3;3~"),
+            ("shift-alt-delete", "\x1b[3;4~"),
+            ("ctrl-delete", "\x1b[3;5~"),
+            ("ctrl-shift-delete", "\x1b[3;6~"),
+            ("ctrl-alt-delete", "\x1b[3;7~"),
+            ("ctrl-shift-alt-delete", "\x1b[3;8~"),
+        ];
+        for (keystroke, expected) in cases {
+            assert_eq!(
+                to_esc_str(&Keystroke::parse(keystroke).unwrap(), Modes::NONE, false),
+                Some(expected.into()),
+                "On keystroke: {}",
+                keystroke
+            );
+        }
+    }
+
     #[test]
     fn test_shift_enter_newline() {
         let shift_enter = Keystroke::parse("shift-enter").unwrap();