refactor(js): golf a bit touch-related js

There is no need to instantiate the whole TouchHandler object to call a single
static method that immediately returns in case touch events aren't supported:
it's better to extract the condition around the calls, so that the object is
never instantiated.

Another change is to replace `() => this.reset()` with `this.reset`, which is
equivalent, but shorted and less weird.

internal/ui/static/js/app.js

@@ -1230,9 +1230,11 @@ function initializeKeyboardShortcuts() {
  * Initialize touch handler for mobile devices.
  */
 function initializeTouchHandler() {
+    if ( "ontouchstart" in window || navigator.maxTouchPoints > 0) {
         const touchHandler = new TouchHandler();
         touchHandler.listen();
     }
+}
 
 /**
  * Initialize click handlers for various UI elements.

internal/ui/static/js/touch_handler.js

@@ -151,35 +151,27 @@ class TouchHandler {
         }
     }
 
-    static isTouchSupported() {
-        return "ontouchstart" in window || navigator.maxTouchPoints > 0;
-    }
-
     listen() {
-        if (!TouchHandler.isTouchSupported()) {
-            return;
-        }
-
         const eventListenerOptions = { passive: true };
 
         document.querySelectorAll(".entry-swipe").forEach((element) => {
             element.addEventListener("touchstart", (e) => this.onItemTouchStart(e), eventListenerOptions);
             element.addEventListener("touchmove", (e) => this.onItemTouchMove(e));
             element.addEventListener("touchend", (e) => this.onItemTouchEnd(e), eventListenerOptions);
-            element.addEventListener("touchcancel", () => this.reset(), eventListenerOptions);
+            element.addEventListener("touchcancel", this.reset, eventListenerOptions);
         });
 
         const element = document.querySelector(".entry-content");
         if (element) {
             if (element.classList.contains("gesture-nav-tap")) {
                 element.addEventListener("touchend", (e) => this.onTapEnd(e), eventListenerOptions);
-                element.addEventListener("touchmove", () => this.reset(), eventListenerOptions);
+                element.addEventListener("touchmove", this.reset, eventListenerOptions);
-                element.addEventListener("touchcancel", () => this.reset(), eventListenerOptions);
+                element.addEventListener("touchcancel", this.reset, eventListenerOptions);
             } else if (element.classList.contains("gesture-nav-swipe")) {
                 element.addEventListener("touchstart", (e) => this.onContentTouchStart(e), eventListenerOptions);
                 element.addEventListener("touchmove", (e) => this.onContentTouchMove(e), eventListenerOptions);
                 element.addEventListener("touchend", (e) => this.onContentTouchEnd(e), eventListenerOptions);
-                element.addEventListener("touchcancel", () => this.reset(), eventListenerOptions);
+                element.addEventListener("touchcancel", this.reset, eventListenerOptions);
             }
         }
     }