[docs] Mention SWC in TypeScript documentation. (vercel#33801)

Update outdated TS/TSX compiler information in the documentation.

## 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
- [x] 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`


Co-authored-by: Lee Robinson <9113740+leerob@users.noreply.github.com>

docs/basic-features/typescript.md

@@ -37,7 +37,9 @@ Next.js will automatically configure this file with default values. Providing yo
 
 You can also provide a relative path to a tsconfig.json file by setting `typescript.tsconfigPath` prop inside your `next.config.js` file.
 
-> Next.js uses Babel to handle TypeScript, which has some [caveats](https://babeljs.io/docs/en/babel-plugin-transform-typescript#caveats), and some [compiler options are handled differently](https://babeljs.io/docs/en/babel-plugin-transform-typescript#typescript-compiler-options).
+Starting in `v12.0.0`, Next.js uses [SWC](https://nextjs.org/docs/advanced-features/compiler) by default to compile TypeScript and TSX for faster builds.
+
+> Next.js will use Babel to handle TypeScript if `.babelrc` is present. This has some [caveats](https://babeljs.io/docs/en/babel-plugin-transform-typescript#caveats) and some [compiler options are handled differently](https://babeljs.io/docs/en/babel-plugin-transform-typescript#typescript-compiler-options).
 
 Then, run `next` (normally `npm run dev` or `yarn dev`) and Next.js will guide you through the installation of the required packages to finish the setup: