[types] fix @stylexjs/babel plugin cjs compat

[henryqdineen]

What changed / motivation ?

In ce530d0 I pushed a fix for a TypeScript error that we were seeing.

node_modules/@stylexjs/babel-plugin/lib/index.d.ts:53:1 - error TS2309: An export assignment cannot be used in a module with other exported elements.

53 export = $$EXPORT_DEFAULT_DECLARATION$$;
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I'm assuming most other's were not hitting this if they set skipLibCheck: true. The v0.16.3 release fixed the error and our StyleX integration works as expected.

I was reading through old issues I discovered #889 and the attempted fix (#924). I think my commit ultimately reverted their fix and likely caused a regression for some people. See: https://arethetypeswrong.github.io/?p=%40stylexjs%2Fbabel-plugin%400.16.3

My fix in this PR is to go back to using export = but use a namespace so we don't run into the "An export assignment cannot be used in a module with other exported elements" error. This commit also corrects the Rule type and config argument for processStylexRules, which have changed since this file was introduced.

Sorry for the regression. Thanks!

Linked PR/Issues

#889

Pre-flight checklist

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  Contribution Guidelines
• Performed a self-review of my code

[nmn]

Can we avoid using a namespace here? Other than that the changes look good.

[henryqdineen]

Thanks @nmn. I was following this advice from the DefinitelyTyped README. Do you have a recommended solution without a namespace?

When the implementation package uses module.exports = ..., the DefinitelyTyped package should use export =, not export default. (Alternatively, if the module.exports is just an object of named properties, the DefinitelyTyped package can use a series of named exports.) The most common obstacle to correcting this problem is confusion about how to export types in addition to the primary export. For example, assume these types are incorrectly using export default:

export interface Options {
    // ...
}
export default function doSomething(options: Options): void;

Changing the export default to an export = creates an error:

export interface Options {
    // ...
}
declare function doSomething(options: Options): void;
export = doSomething;
// ^^^^^^^^^^^^^^^^^
// Error: An export assignment cannot be used in a module with other exported elements.

To fix this, move the types inside a namespace with the same name as the function:

declare namespace doSomething {
    export interface Options {
        // ...
    }
}
declare function doSomething(options: doSomething.Options): void;
export = doSomething;

[nmn]

I wonder if you can use this type and use the export = syntax to make it work with cjs?

[henryqdineen]

I can't seem to find a way to do it with running in to "An export assignment cannot be used in a module with other exported elements.(2309)"