RFC: Show loading.js for client navigations even if prefetching is disabled, if the target page has same route as the current page

[remorses]

Goals

Currently loading.js placeholder pages only show up on client navigation if the target route has been prefetched. This is not ideal in a website with many links (for example in a docs website with a sidebar).

Prefetching links before showing loading.js shouldn't be needed If the navigated page is the same as the current one.
For example let's say the current page is [[...slug]].js, the user navigates to another page in [[...slug]].js. If the target page has not been prefetched the loading.js skeleton won't be shown.

But given that the loading.js is the same for all [[...slug]].js pages there is no need to prefetch these links before showing the skeleton, because this component should already be available.

Goals:

1. Make it possible to show loading.js even if prefetching is disabled
2. Make it possible to show loading.js even if prefetching hasn't completed

Non-Goals

No response

Background

I am building a docs website where there are many links on the page, i want to disable prefetching to not trigger tons of requests on the first load but by disabling prefetching the user can no longer see the loading.js skeleton.

Proposal

Use the already available loading.js component if the navigated page uses the same loading.js as the current one (same route, for example [[...slug]].js)