feat(tech): add a scrubbing getter. (#6920)

This is helpful for source handlers and anything else that could have
customer behavior for when we're scrubbing or not.

Author: gkatsev

src/js/tech/html5.js

@@ -54,6 +54,8 @@ class Html5 extends Tech {
       this.setupSourcesetHandling_();
     }
 
+    this.isScrubbing_ = false;
+
     if (this.el_.hasChildNodes()) {
 
       const nodes = this.el_.childNodes;
@@ -537,6 +539,17 @@ class Html5 extends Tech {
     this.isScrubbing_ = isScrubbing;
   }
 
+  /**
+   * Get whether we are scrubbing or not.
+   *
+   * @return {boolean} isScrubbing
+   *                  - true for we are currently scrubbing
+   *                  - false for we are no longer scrubbing
+   */
+  scrubbing() {
+    return this.isScrubbing_;
+  }
+
   /**
    * Set current time for the `HTML5` tech.
    *

src/js/tech/tech.js

@@ -501,6 +501,15 @@ class Tech extends Component {
    */
   setScrubbing() {}
 
+  /**
+   * Get whether we are scrubbing or not
+   *
+   * @abstract
+   *
+   * @see {Html5#scrubbing}
+   */
+  scrubbing() {}
+
   /**
    * Causes a manual time update to occur if {@link Tech#manualTimeUpdatesOn} was
    * previously called.