Can't be used within browser manifest v3 service workers

**Describe the bug**

If a developer wants to use this library within a service worker (enforced in Manifest V3 extension spec sadly), it will not work due to the dependencies around `document` in `resolve-url` library. Neither `window` nor `document` is available inside a service worker.

I tried to remove the `resolve-url` dependency, but then I discovered that `URL.createObjectURL` is not available within service workers and it is [required in `getCreateFFmpegCore`](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/master/src/browser/getCreateFFmpegCore.js#L17). Perhaps there is a way to remove its dependency?

If you are debugging, you might need to change `browser/fetchFile.js` to something similar to the `node/fetchFile.js`, but without the `fs` and `util` imports.

```js
const isURL = require('is-url');

module.exports = async (_data) => {
let data = _data;
if (typeof _data === 'undefined') {
return new Uint8Array();
}

if (typeof _data === 'string') {
/* From remote URL/server */
if (isURL(_data)
|| _data.startsWith('moz-extension://')
|| _data.startsWith('chrome-extension://')
|| _data.startsWith('file://')) {
const res = await fetch(_data);
data = await res.arrayBuffer();
/* From base64 format */
} else if (/data:_data\/([a-zA-Z]*);base64,([^"]*)/.test(_data)) {
data = Buffer.from(_data.split(',')[1], 'base64');
/* From local file path */
}
/* From Buffer */
} else if (Buffer.isBuffer(_data)) {
data = _data;
}

return new Uint8Array(data);
};
```

**To Reproduce**
Steps to reproduce the behavior:
1. Create a basic chrome extension with
```json
{
"manifest_version": 3,
"version": "1.0.0",
"name": "Test Extension",
"author": "Bruno Luiz Silva ",
"web_accessible_resources": [
{
"resources": [ "src/vendor/*" ],
"matches": ["*://*/*"]
}
],
"background": {
"service_worker": "src/js/background.js"
},
"host_permissions": [
"*://*/*"
],
"content_security_policy": {
"extension_pages": "default-src 'self'; media-src * blob:"
},
"cross_origin_embedder_policy": {
"value": "require-corp"
},
"cross_origin_opener_policy": {
"value": "same-origin"
}
}
```

2. Place ffmpeg and ffmpeg-core dist files within `src/vendor`
3. Create a `src/js/background.js` file
```js
(async () => {
try {
importScripts("/src/vendor/ffmpeg-core.js", "/src/vendor/ffmpeg.min.js");
} catch (e) {
console.error(e);
}

const corePath = chrome.runtime.getURL("src/vendor/ffmpeg-core.js");
const settings = { corePath, log: true };

ffmpeg = await FFmpeg.createFFmpeg(settings);
await ffmpeg.load();
})();

```
5. Load unpacked extension in Chrome
6. Get an error message in the service worker console (click on `Inspect Views` in the loaded extension)

**Expected behavior**

Work within browser service workers, albeit it was only tested within manifest v3 service workers.

**Screenshots**

**Desktop (please complete the following information):**
- OS: MacOS 12.1
- Browser Chrome
- Version Version 96.0.4664.110 (Official Build) (x86_64)