DNin/wake-lock: Reacquire wake lock as needed (#1158)

Resolves #1120

Currently, if you request a wake lock with the Wake Lock extension and
then navigate away from the page, the wake lock gets released in the
background because wake locks are automatically released when the
document gets hidden, plus, the extension isn't aware of when this
happens, so you have no way of knowing.

This change makes the extension automatically request another wake lock
when the document regains visibility after having been hidden. It still
reports to the project that the wake lock is enabled when this happens,
therefore projects will act like nothing happened but the wake lock will
still be there as long as you come back. I also considered the
possibility of projects enabling or disabling wake lock when the
document is hidden and now handle it properly.

I tested these changes in Edge to the best of my ability.

extensions/DNin/wake-lock.js

@@ -19,6 +19,16 @@
     constructor(runtime) {
       this.runtime = runtime;
       this.runtime.on("PROJECT_STOP_ALL", this.stopAll.bind(this));
+
+      document.addEventListener("visibilitychange", () => {
+        // If enabled, reacquire wake lock when document becomes visible again
+        if (wakeLock !== null && document.visibilityState === "visible") {
+          latestEnabled = false;
+          this.setWakeLock({
+            enabled: true,
+          });
+        }
+      });
     }
 
     getInfo() {
@@ -77,14 +87,26 @@
         // Not supported in this browser.
         return;
       }
+      const enable = Scratch.Cast.toBoolean(args.enabled);
+      if (enable && document.visibilityState === "hidden") {
+        // Can't request wake lock while document is hidden.
+        return;
+      }
 
       const previousEnabled = latestEnabled;
-      latestEnabled = Scratch.Cast.toBoolean(args.enabled);
+      latestEnabled = enable;
       if (latestEnabled && !previousEnabled) {
         promise = promise
           .then(() => navigator.wakeLock.request("screen"))
           .then((sentinel) => {
             wakeLock = sentinel;
+            wakeLock.addEventListener("release", () => {
+              if (document.visibilityState === "visible") {
+                // If the document is hidden, wake lock should be reacquired when it's visible again.
+                wakeLock = null;
+                latestEnabled = false;
+              }
+            });
           })
           .catch((error) => {
             console.error(error);