chore: export default and named packages

[SethFalco]

Makes three minor changes.

1. Include VERSION in the type definition, this was missed before.
2. Make it so SVGO exports both default and named exports. (For a consistent interface between require and import.)
3. Change the version in package.json to 4.0.0-rc.0.

For more context on exports, this ensures a more consistent API between CJS and ESM, see the following:

// default.mjs
import SVGO from 'svgo'; // not possible before
console.log(SVGO.VERSION); // 4.0.0-rc.0

// destruct.mjs
import { VERSION } from 'svgo';
console.log(VERSION);  // 4.0.0-rc.0

// default.cjs
const SVGO = require('svgo');
console.log(SVGO.VERSION);  // 4.0.0-rc.0

// destruct.cjs
const { VERSION } = require('svgo');
console.log(VERSION); // 4.0.0-rc.0

// browser.mjs
import SVGO from 'svgo/browser';
console.log(SVGO.VERSION); // 4.0.0-rc.0