Add docs for the Next.js Compiler written in Rust (leveraging SWC)

[timneutkens]

Follow-up to #31467 with reworked wording.

Fixes #20619

• Rust Compiler -> Next.js Compiler. Given that it is not SWC exactly and not "Compiling Rust" the "Next.js Compiler" makes more sense. next-swc could also be used as that's what we named the package.
• Removed mention of "Supported features" as it implies those are the only things it does, and these are Next.js features which you'd expect to just work no matter the underlaying implementation
• Removed the list from "Unsupported Features" as it implies they will never be supported and the list is not complete. The list mentioned are transforms we're actually going to work on soon. Linking to the discussions thread instead works here because this is a moving target as we're implementing improvements and items on the list every day currently.
• Add swcMinify feedback link to ensure we keep collecting feedback if people run into issues with it
• Reworked the styled-components section a bit to explain that the 2 transforms mentioned are all that is required in general. Also options -> transforms given that Next.js auto-configures the right options for it and you can't configure those transforms individually.
• Updated all cases where installing canary is mentioned as all the mentioned transforms are out on stable now in 12.0.4 (they're still experimental though) 🎉
• Reworded the mention of mobx to say "older versions of mobx" as it's no longer recommended in the mobx docs

Bug

• Related issues linked using fixes #number
• Integration tests added
• Errors have helpful link attached, see contributing.md

Feature

• Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
• Related issues linked using fixes #number
• Integration tests added
• Documentation added
• Telemetry added. In case of a feature if it's used or not.
• Errors have helpful link attached, see contributing.md

Documentation / Examples

• Make sure the linting passes by running yarn lint