Allow mapping new-style sequences that start with escape

On Konsole with

    function my-bindings
        bind --preset --erase escape
        bind escape,i 'echo escape i'
    end
    set fish_key_bindings my-bindings

the "escape,i" binding doesn't trigger.  This is because of our special
handling of the escape key prefix.  Other multi-key bindings like "bind j,k"
wait indefinitely for the second character.  But not "escape,i"; that one
has historically had a low timeout (fish_escape_delay_ms).  The motivation
is probably that we have a "escape" binding as well that shouldn't wait
indefinitely.

We can distinguish between the case of raw escape sequence binding like "\e123"
and a binding that talks about the actual escape key like "escape,i". For the
latter we don't need the special treatment of having a low timeout, so make it
fall back to "fish_sequence_key_delay_ms" which waits indefinitely by default.

src/input.rs

@@ -653,15 +653,26 @@ fn next_is_char(&mut self, style: &KeyNameStyle, key: Key, escaped: bool) -> boo
         // Grab a new event if we have exhausted what we have already peeked.
         // Use either readch or readch_timed, per our param.
         if self.idx == self.peeked.len() {
-            let Some(newevt) = (if escaped {
+            let newevt = if escaped {
                 FLOG!(reader, "reading timed escape");
-                self.event_queue.readch_timed_esc()
+                match self.event_queue.readch_timed_esc(style) {
+                    Ok(evt) => evt,
+                    Err(timed_out) => {
+                        if timed_out {
+                            self.had_timeout = true;
+                        }
+                        return false;
+                    }
+                }
             } else {
                 FLOG!(reader, "readch timed sequence key");
-                self.event_queue.readch_timed_sequence_key()
-            }) else {
-                self.had_timeout = true;
-                return false;
+                match self.event_queue.readch_timed_sequence_key() {
+                    Some(evt) => evt,
+                    None => {
+                        self.had_timeout = true;
+                        return false;
+                    }
+                }
             };
             FLOG!(reader, format!("adding peeked {:?}", newevt));
             self.peeked.push(newevt);