refactor(pwa): revert to JS and Liquid mixing

The gem package won't be able to pass `/sw.min.js` to the user end

assets/js/pwa/app.js

@@ -0,0 +1,54 @@
+---
+layout: compress
+permalink: /assets/js/dist/:basename.min.js
+---
+
+if ('serviceWorker' in navigator) {
+  const isEnabled = '{{ site.pwa.enabled }}' === 'true';
+
+  if (isEnabled) {
+    const swUrl = '{{ '/sw.min.js' | relative_url }}';
+    const $notification = $('#notification');
+    const $btnRefresh = $('#notification .toast-body>button');
+
+    navigator.serviceWorker.register(swUrl).then((registration) => {
+      {% comment %}In case the user ignores the notification{% endcomment %}
+      if (registration.waiting) {
+        $notification.toast('show');
+      }
+
+      registration.addEventListener('updatefound', () => {
+        registration.installing.addEventListener('statechange', () => {
+          if (registration.waiting) {
+            if (navigator.serviceWorker.controller) {
+              $notification.toast('show');
+            }
+          }
+        });
+      });
+
+      $btnRefresh.on('click', () => {
+        if (registration.waiting) {
+          registration.waiting.postMessage('SKIP_WAITING');
+        }
+        $notification.toast('hide');
+      });
+    });
+
+    let refreshing = false;
+
+    {% comment %}Detect controller change and refresh all the opened tabs{% endcomment %}
+    navigator.serviceWorker.addEventListener('controllerchange', () => {
+      if (!refreshing) {
+        window.location.reload();
+        refreshing = true;
+      }
+    });
+  } else {
+    navigator.serviceWorker.getRegistrations().then(function (registrations) {
+      for (let registration of registrations) {
+        registration.unregister();
+      }
+    });
+  }
+}