Dashboard: Add new visualization/row/library panel/pasted panel is now a dropdown menu (#65361)

* Empty Dashboard state has its own CTA items and its own separate box to choose a library panel to create

* show empty dashboard screen if no panels

* add feature flag for empty dashboard redesign

* only show empty dashboard redesign if FF

* add-new-panel button is a dropdown with options: visualization, row, import, paste

* fix onPasteCopiedPanel types

* do not create new panel to new dashboard if emptyDashboardPage FF true

* ToolbarButton does not allow rendering of Dropdown's overlay - switch to Button

* remove panel-add icon's default size of xl

* separate components for add new panel from dash navigation bar

packages/grafana-ui/src/components/Icon/Icon.tsx

@@ -45,10 +45,6 @@ export const Icon = React.forwardRef<HTMLDivElement, IconProps>(
       return <i className={getFontAwesomeIconStyles(name, className)} {...divElementProps} style={style} />;
     }
 
-    if (name === 'panel-add') {
-      size = 'xl';
-    }
-
     if (!cacheInitialized) {
       initIconCache();
     }