`registerActiveTabScripts` - allow filtering out some tabs

To restore some functionality from https://github.com/fregante/webext-dynamic-content-scripts/pull/78

Static

```diff
import registerActiveTabScripts from 'webext-active-tab/register-active-tab-scripts';
+ import {isContentScriptRegistered} from 'webext-dynamic-content-scripts/utils.js';

registerActiveTabScripts({
+ filter: async tab => !isContentScriptRegistered(tab.url),
js: [
'content.js',
],
css: [
'content.css',
],

runAt: 'document_idle',
matchAboutBlank: false,
});
```

Start at the register-active-tab-scripts entry point shown in the issue and inspect how its options are handled. Add support for the proposed asynchronous filter option so matching tabs can be skipped, then verify that the example using isContentScriptRegistered behaves as intended; no test file is named in the issue.

Written by the indexing model from the issue text.