Deadkeys 2 (#20612)

Re-land of #20515 with less brokenness

In particular it turns out that for control, the .characters() method
returns the control code. This mostly didn't make a difference, except
when the control code matched tab/enter/escape (for
ctrl-y,ctrl-[/ctrl-c) as we interpreted the key incorrectly.

Secondly, we were setting IME key too aggressively. This led to (in vim
mode) cmd-shift-{ being interpreted as [, so vim would wait for a second
[ before letting you change tab.

Release Notes:

- N/A

crates/terminal_view/src/terminal_element.rs

@@ -1044,6 +1044,10 @@ impl InputHandler for TerminalInputHandler {
     ) -> Option<Bounds<Pixels>> {
         self.cursor_bounds
     }
+
+    fn apple_press_and_hold_enabled(&mut self) -> bool {
+        false
+    }
 }
 
 pub fn is_blank(cell: &IndexedCell) -> bool {