[Dashboard Navigation] Add external link icon (elastic#174407)

Closes elastic#165771

## Summary

This PR adds the `external` prop to links in the Link panel in the
following cases:
1. A dashboard link has the "Open in new tab" setting set to `true`
2. All URLs, regardless of if the "Open in new tab" setting is set to
`true` or `false`

This `external` prop renders the popout icon beside the links, like so:


![linksExternalProp](https://github.com/elastic/kibana/assets/8698078/3bc1ea05-fffd-455a-a4e3-81456bb6b024)



### Checklist

- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [x] Any UI touched in this PR is usable by keyboard only (learn more
about [keyboard accessibility](https://webaim.org/techniques/keyboard/))
- [x] Any UI touched in this PR does not create any new axe failures
(run axe in browser:
[FF](https://addons.mozilla.org/en-US/firefox/addon/axe-devtools/),
[Chrome](https://chrome.google.com/webstore/detail/axe-web-accessibility-tes/lhdoppojpmngadmnindnejefpokejbdd?hl=en-US))
- [x] This renders correctly on smaller devices using a responsive
layout. (You can test this [in your
browser](https://www.browserstack.com/guide/responsive-testing-on-local-server))
- [x] This was checked for [cross-browser
compatibility](https://www.elastic.co/support/matrix#matrix_browsers)


### For maintainers

- [ ] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

src/plugins/links/public/components/dashboard_link/dashboard_link_component.test.tsx

@@ -11,7 +11,7 @@ import React from 'react';
 import { getDashboardLocatorParamsFromEmbeddable } from '@kbn/dashboard-plugin/public';
 import { DashboardContainer } from '@kbn/dashboard-plugin/public/dashboard_container';
 import { DEFAULT_DASHBOARD_DRILLDOWN_OPTIONS } from '@kbn/presentation-util-plugin/public';
-import { createEvent, fireEvent, render, screen, waitFor } from '@testing-library/react';
+import { createEvent, fireEvent, render, screen, waitFor, within } from '@testing-library/react';
 import userEvent from '@testing-library/user-event';
 
 import { LINKS_VERTICAL_LAYOUT } from '../../../common/content_management';
@@ -104,8 +104,15 @@ describe('Dashboard link component', () => {
     expect(fetchDashboard).toHaveBeenCalledWith(defaultLinkInfo.destination);
     await waitFor(() => expect(onRender).toHaveBeenCalledTimes(1));
 
+    // renders dashboard title
     const link = await screen.findByTestId('dashboardLink--foo');
     expect(link).toHaveTextContent('another dashboard');
+
+    // does not render external link icon
+    const externalIcon = within(link).queryByText('External link');
+    expect(externalIcon).toBeNull();
+
+    // calls `navigate` on click
     userEvent.click(link);
     expect(dashboardContainer.locator?.getRedirectUrl).toBeCalledWith({
       dashboardId: '456',
@@ -134,7 +141,7 @@ describe('Dashboard link component', () => {
     expect(preventDefault).toHaveBeenCalledTimes(0);
   });
 
-  test('openInNewTab uses window.open, not navigateToApp', async () => {
+  test('openInNewTab uses window.open, not navigateToApp, and renders external icon', async () => {
     const linkInfo = {
       ...defaultLinkInfo,
       options: { ...DEFAULT_DASHBOARD_DRILLDOWN_OPTIONS, openInNewTab: true },
@@ -155,6 +162,12 @@ describe('Dashboard link component', () => {
     await waitFor(() => expect(onRender).toHaveBeenCalledTimes(1));
     const link = await screen.findByTestId('dashboardLink--foo');
     expect(link).toBeInTheDocument();
+
+    // external link icon is rendered
+    const externalIcon = within(link).getByText('External link');
+    expect(externalIcon?.getAttribute('data-euiicon-type')).toBe('popout');
+
+    // calls `window.open`
     userEvent.click(link);
     expect(dashboardContainer.locator?.navigate).toBeCalledTimes(0);
     expect(window.open).toHaveBeenCalledWith('https://my-kibana.com/dashboard/123', '_blank');

src/plugins/links/public/components/dashboard_link/dashboard_link_component.tsx

@@ -187,6 +187,7 @@ export const DashboardLinkComponent = ({
         'dashboardLinkError--noLabel': !link.label,
       })}
       label={linkLabel}
+      external={link.options?.openInNewTab}
       data-test-subj={error ? `${id}--error` : `${id}`}
     />
   );

src/plugins/links/public/components/external_link/external_link_component.test.tsx

@@ -9,7 +9,7 @@
 import React from 'react';
 
 import userEvent from '@testing-library/user-event';
-import { createEvent, fireEvent, render, screen } from '@testing-library/react';
+import { createEvent, fireEvent, render, screen, within } from '@testing-library/react';
 import { LinksEmbeddable, LinksContext } from '../../embeddable/links_embeddable';
 import { mockLinksPanel } from '../../../common/mocks';
 import { LINKS_VERTICAL_LAYOUT } from '../../../common/content_management';
@@ -37,7 +37,7 @@ describe('external link component', () => {
     jest.clearAllMocks();
   });
 
-  test('by default opens in new tab', async () => {
+  test('by default opens in new tab and renders external icon', async () => {
     render(
       <LinksContext.Provider value={links}>
         <ExternalLinkComponent
@@ -51,10 +51,27 @@ describe('external link component', () => {
     expect(onRender).toBeCalledTimes(1);
     const link = await screen.findByTestId('externalLink--foo');
     expect(link).toBeInTheDocument();
-    await userEvent.click(link);
+    const externalIcon = within(link).getByText('External link');
+    expect(externalIcon.getAttribute('data-euiicon-type')).toBe('popout');
+    userEvent.click(link);
     expect(window.open).toHaveBeenCalledWith('https://example.com', '_blank');
   });
 
+  test('renders external icon even when `openInNewTab` setting is `false`', async () => {
+    const linkInfo = {
+      ...defaultLinkInfo,
+      options: { ...DEFAULT_URL_DRILLDOWN_OPTIONS, openInNewTab: false },
+    };
+    render(
+      <LinksContext.Provider value={links}>
+        <ExternalLinkComponent link={linkInfo} layout={LINKS_VERTICAL_LAYOUT} onRender={onRender} />
+      </LinksContext.Provider>
+    );
+    const link = await screen.findByTestId('externalLink--foo');
+    const externalIcon = within(link).getByText('External link');
+    expect(externalIcon?.getAttribute('data-euiicon-type')).toBe('popout');
+  });
+
   test('modified click does not trigger event.preventDefault', async () => {
     const linkInfo = {
       ...defaultLinkInfo,
@@ -86,7 +103,7 @@ describe('external link component', () => {
     );
     expect(onRender).toBeCalledTimes(1);
     const link = await screen.findByTestId('externalLink--foo');
-    await userEvent.click(link);
+    userEvent.click(link);
     expect(coreServices.application.navigateToUrl).toBeCalledTimes(1);
     expect(coreServices.application.navigateToUrl).toBeCalledWith('https://example.com');
   });

src/plugins/links/public/components/external_link/external_link_component.tsx

@@ -65,6 +65,7 @@ export const ExternalLinkComponent = ({
   return (
     <EuiListGroupItem
       size="s"
+      external
       color="text"
       isDisabled={!link.destination || !isValidUrl}
       className={'linksPanelLink'}