EV3/Microbit critical fixes for code freeze (#1354)

* Resolves - BLESession and BTSession should emit PERIPHERAL_SCAN_TIMEOUT #1348.

* Resolves - BLESession should handle 'could not find service' error #1350.

* Resolves - BTSession should handle 'no peripheral connected' error #1351.

* Fixing a typo that caused device scan timeout bugs.

* Resolves - Add casting and clamping throughout the EV3 extension #1352.

* Fixing a linting error.

* Further fixes for issue #1351.

src/engine/runtime.js

@@ -428,6 +428,14 @@ class Runtime extends EventEmitter {
         return 'PERIPHERAL_ERROR';
     }
 
+    /**
+     * Event name for reporting that a peripheral has not been discovered.
+     * @const {string}
+     */
+    static get PERIPHERAL_SCAN_TIMEOUT () {
+        return 'PERIPHERAL_SCAN_TIMEOUT';
+    }
+
     /**
      * Event name for reporting that blocksInfo was updated.
      * @const {string}