[NEXT-1184] moving focus after navigations

### Verify canary release - [X] I verified that the issue exists in the latest Next.js canary release ### Provide environment information ```bash N/A ``` ### Which area(s) of Next.js are affected? (leave empty if unsure) App directory (appDir: true), Routing (next/router, next/navigation, next/link) ### Link to the code that reproduces this issue https://github.com/vercel/app-playground ### To Reproduce Open any Nextjs app, click on any link, then inspect focus - it stays on the link or gets lost if link is no longer on the page. This is more obvious to see if you use keyboard to <kbd>Tab</kbd> to any link then press <kbd>Enter</kbd>. ### Describe the Bug I've been keeping my eye on the App Router roadmap since it said "Accessibility". Now that it is stable, I see that it announces the page title on every navigation. This is a great first step! However, this is _not_ enough most of the times. Consider a basic example of a documentation website containing a sidebar and a content area. Now if a keyboard user navigates to a different page using a link in the sidebar, the focus stays on that link even after navigation; any "skip-to-content" links that would normally be near the top of the page (and therefore quick to find) are now several tab stops away. And this is assuming the link is even on the page; if it's not then the focus will get _lost_, which is not ideal at all. When you look at a regular (non-SPA) website, the browser will reset focus to the top of the page after navigation instead of leaving it somewhere in the middle. This makes sense because it's a new page. Since Nextjs is trying to recreate navigations using client-side JavaScript, I think it would similarly make sense to simulate browser behavior and reset focus. However, even this may not be ideal in complex dynamic apps with nested layouts, because a screen-reader/keyboard user would have to tediously traverse through the lots of elements to get to the part that actually changed. The "best" solution…