@ffmpeg/core and @ffmpeg/core-mt missing export for the ffmpeg-core.worker.js file.

**Describe the bug**
From the `@ffmpeg/core`, `@ffmpeg/core-mt` it is not possible to import the ffmpeg-core.worker.js with the import directive.

**To Reproduce**
```js
import ffmpegCoreUrl from '@ffmpeg/core-mt?url';
import ffmpegWasmUrl from '@ffmpeg/core-mt/wasm?url';
import ffmpegWorkerUrl from '@ffmpeg/core-mt/worker?url'; //Missing

await ffmpeg.load({
coreURL: await toBlobURL(ffmpegCoreUrl, 'text/javascript'),
wasmURL: await toBlobURL(ffmpegWasmUrl, 'application/wasm'),
workerURL: await toBlobURL(ffmpegWorkerUrl, 'text/javascript')
});
```

**Expected behavior**
Something like this should load the files.

**Additional context**
This is required for asset bundlers to resolve the urls, like Vite.
The worker in package.json should solve the issue.

```json
"exports": {
".": {
"import": "./dist/esm/ffmpeg-core.js",
"require": "./dist/umd/ffmpeg-core.js"
},
"./wasm": {
"import": "./dist/esm/ffmpeg-core.wasm",
"require": "./dist/umd/ffmpeg-core.wasm"
},
"./worker": {
"import": "./dist/esm/ffmpeg-core.worker.js",
"require": "./dist/umd/ffmpeg-core.worker.js"
}
},
```