fix(tech): add abstract setScrubbing in tech.js (#6808)

src/js/tech/html5.js

@@ -524,6 +524,15 @@ class Html5 extends Tech {
     });
   }
 
+  /**
+   * Set whether we are scrubbing or not.
+   * This is used to decide whether we should use `fastSeek` or not.
+   * `fastSeek` is used to provide trick play on Safari browsers.
+   *
+   * @param {boolean} isScrubbing
+   *                  - true for we are currently scrubbing
+   *                  - false for we are no longer scrubbing
+   */
   setScrubbing(isScrubbing) {
     this.isScrubbing_ = isScrubbing;
   }

src/js/tech/tech.js

@@ -483,6 +483,15 @@ class Tech extends Component {
     return createTimeRange();
   }
 
+  /**
+   * Set whether we are scrubbing or not
+   *
+   * @abstract
+   *
+   * @see {Html5#setScrubbing}
+   */
+  setScrubbing() {}
+
   /**
    * Causes a manual time update to occur if {@link Tech#manualTimeUpdatesOn} was
    * previously called.