feat(toolbar-button-clicked) Enhance toolbar buttons with notify click

- add possibility to allow execution of the button's routine besides triggering
`toolbarButtonClicked` API event
- keep backwards compatibility
- get rid of `ToolbarButton`

react/features/toolbox/components/web/ShareDesktopButton.js

@@ -67,22 +67,6 @@ class ShareDesktopButton extends AbstractButton<Props, *> {
         // Unused.
     }
 
-    /**
-     * Handles clicking / pressing the button, and opens the appropriate dialog.
-     *
-     * @protected
-     * @returns {void}
-     */
-    _handleClick() {
-        const { handleClick } = this.props;
-
-        if (handleClick) {
-            handleClick();
-
-            return;
-        }
-    }
-
     /**
      * Indicates whether this button is in toggled state or not.
      *