Use named constants for magic numbers (#19992)

Mostly KeyboardEvent.which and MouseEvent.which values.

[skip validator]

js/src/modal.js

@@ -25,6 +25,7 @@ const Modal = (($) => {
   const JQUERY_NO_CONFLICT           = $.fn[NAME]
   const TRANSITION_DURATION          = 300
   const BACKDROP_TRANSITION_DURATION = 150
+  const ESCAPE_KEYCODE               = 27 // Escape (Esc) key
 
   const Default = {
     backdrop : true,
@@ -271,7 +272,7 @@ const Modal = (($) => {
     _setEscapeEvent() {
       if (this._isShown && this._config.keyboard) {
         $(this._element).on(Event.KEYDOWN_DISMISS, (event) => {
-          if (event.which === 27) {
+          if (event.which === ESCAPE_KEYCODE) {
             this.hide()
           }
         })