[docs] Clarify polyfill support

[josh-]

Currently next.js polyfills a subset of APIs for nomodule browsers (such as IE 11), however it's not immediately clear to developers which APIs are transparently polyfilled.

For example, currently Object.entries is polyfilled and thus is usable in IE 11, but it was decided that Object.fromEntries should not be polyfilled. As a developer, this is a confusing situation until you end up finding the next-polyfill-nomodule list of polyfills that are included.

This PR attempts to improve the Supported Browser Features page by:

• linking to the list of polyfills
• clarifying that custom polyfills are required for IE11 (and other old browser) compatibility
• moving the section on Sever-Side polyfills further down the page so all browser polyfill sections are better grouped together

Documentation / Examples

• Make sure the linting passes by running pnpm lint
• The examples guidelines are followed from our contributing doc

[leerob]

This looks good. We might also want to add this from 12.2

We've added experimental support for shipping only modern JavaScript by modifying browsersList. You can opt-into this behavior by setting browsersListForSwc: true and legacyBrowsers: false in the experimental option of next.config.js.

[josh-]

Thanks @leerob! 🎉