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/etherpad/components/SharedDocumentButton.web.js

@@ -9,7 +9,6 @@ import { connect } from '../../base/redux';
 import { AbstractButton, type AbstractButtonProps } from '../../base/toolbox/components';
 import { toggleDocument } from '../../etherpad/actions';
 
-
 type Props = AbstractButtonProps & {
 
     /**
@@ -59,13 +58,7 @@ class SharedDocumentButton extends AbstractButton<Props, *> {
      * @returns {void}
      */
     _handleClick() {
-        const { _editing, dispatch, handleClick } = this.props;
-
-        if (handleClick) {
-            handleClick();
-
-            return;
-        }
+        const { _editing, dispatch } = this.props;
 
         sendAnalytics(createToolbarEvent(
             'toggle.etherpad',