[Feature]: Support web-worker

[SoonIter]

What problem does this feature solve?

the bundleless workaround

defineConfig({
lib: [{
  bundle: false,
  format: 'esm',
      syntax: 'esnext',
      tools: {
        rspack: {
          module: {
            parser: {
              javascript: {
                worker: false,
              },
            },
          },
        },
      },
}]
})

but in bundle mode

there are tons of webpack runtime

What does the proposed API look like?

test demo: https://github.com/SoonIter/rslib-worker-demo

in bundle the output should be:

index.js
fib-worker.js
chat-worker.js

// ...
const chatWorker = new SharedWorker(new URL('./chat-worker.js', import.meta.url), {
    name: 'chat',
    type: 'module'
});
// ...
const fibWorker = new Worker(new URL('./fib-worker.js', import.meta.url), {
    name: 'fibonacci',
    type: 'module'
});

[Timeless0911]

After #959, users can set multiple entries like index and worker to achieve this.

We should enhance this to support split worker chunks without webpack runtime when only index entry is configured in the near future.