Fix generated type declarations

[sirreal]

Fix the generated type declarations.

By using TypeScript's special export = we're able to author source that mostly looks like ESM but generates our desired declaration and js output.

The published type declarations are currently export {}, which makes it hard to use this package in typechecked files.

After this change, the generated JS file is mostly the same, but the declaration file has the expected output:

import { JsMinifyOptions } from '@swc/core';
import webpack from 'webpack';
declare class SwcMinifyWebpackPlugin {
    private readonly options;
    constructor(options?: JsMinifyOptions);
    apply(compiler: webpack.Compiler): void;
    private transformAssets;
    private processAssets;
}
export = SwcMinifyWebpackPlugin;

Another change that may be helpful to use a shared tsconfig designed for node, for example:

https://github.com/tsconfig/bases#node-lts--strictest-tsconfigjson

That will likely improve the build result and save generating compatibility code that's not necessary for targeting Node.

I'd be happy to push that here or in another PR.

[guoyunhe]

Released in 1.1.1

[sirreal]

The new releases have the same problem, the published declarations are an empty export. At 1e03fee111c36abd05646d6b99cc31536b053130 (merge commit) this generated the expected declarations.