Change ALT + UP to close the dropdown instead of opening it

This closes https://github.com/select2/select2/issues/3471.

src/js/select2/core.js

@@ -298,7 +298,12 @@ define([
       var key = evt.which;
 
       if (self.isOpen()) {
-        if (key === KEYS.ENTER) {
+        if (key === KEYS.ESC || key === KEYS.TAB ||
+            (key === KEYS.UP && evt.altKey)) {
+          self.close();
+
+          evt.preventDefault();
+        } else if (key === KEYS.ENTER) {
           self.trigger('results:select');
 
           evt.preventDefault();
@@ -313,15 +318,11 @@ define([
         } else if (key === KEYS.DOWN) {
           self.trigger('results:next');
 
-          evt.preventDefault();
-        } else if (key === KEYS.ESC || key === KEYS.TAB) {
-          self.close();
-
           evt.preventDefault();
         }
       } else {
         if (key === KEYS.ENTER || key === KEYS.SPACE ||
-            ((key === KEYS.DOWN || key === KEYS.UP) && evt.altKey)) {
+            (key === KEYS.DOWN && evt.altKey)) {
           self.open();
 
           evt.preventDefault();