vercel / next.js

Closes #16633

- The docs and examples that use `as` have been updated to show how `href` can be used to get the same results
- Added new examples and provided more details on current examples for more details on how `href` can be used.

**Note:** With this change the usage of `as` becomes completely unrequired as I failed to find a good use case for it. Therefore documentation for `as` now includes: `Used for dynamic routes before Next.js 9.5.3`. But that should link to somewhere, either to a blog post or to the Upgrade Guide in our docs.