Sidebar refactor: scope css + more (#20837)

* refactor sidebar, scope css, wire up nav events to link component, update tests

* remove link onClick analytics event

* fix: missing key on breadcrumbs

tests/browser/browser.js

@@ -462,7 +462,9 @@ describe.skip('next/link client-side navigation', () => {
         response.url().startsWith('http://localhost:4001/_next/data')
       ),
       page.waitForNavigation({ waitUntil: 'networkidle2' }),
-      page.click('.sidebar-articles:nth-child(2) .sidebar-article:nth-child(1) a'),
+      page.click(
+        '[data-testid=sidebar-article-group]:nth-child(2) [data-testid=sidebar-article]:nth-child(1) a'
+      ),
     ])
 
     expect(response.status()).toBe(200)