Add Encrypted Media Extensions HDCP Version Registry (#1420)

Close #1419, adding the suggested spec to the list.

### Changes to `index.json`
This update would trigger the following changes in `index.json`:

<details><summary>Add spec (1)</summary>

```json
{
  "url": "https://www.w3.org/TR/eme-hdcp-version-registry/",
  "seriesComposition": "full",
  "shortname": "eme-hdcp-version-registry",
  "series": {
    "shortname": "eme-hdcp-version-registry",
    "currentSpecification": "eme-hdcp-version-registry",
    "title": "Encrypted Media Extensions HDCP Version Registry",
    "shortTitle": "Encrypted Media Extensions HDCP Version Registry",
    "releaseUrl": "https://www.w3.org/TR/eme-hdcp-version-registry/",
    "nightlyUrl": "https://w3c.github.io/encrypted-media/hdcp-version-registry.html"
  },
  "nightly": {
    "url": "https://w3c.github.io/encrypted-media/hdcp-version-registry.html",
    "status": "Editor's Draft",
    "sourcePath": "hdcp-version-registry-respec.html",
    "alternateUrls": [],
    "repository": "https://github.com/w3c/encrypted-media",
    "filename": "hdcp-version-registry.html"
  },
  "organization": "W3C",
  "groups": [
    {
      "name": "Media Working Group",
      "url": "https://www.w3.org/media-wg/"
    }
  ],
  "release": {
    "url": "https://www.w3.org/TR/eme-hdcp-version-registry/",
    "status": "Draft Registry",
    "filename": "Overview.html"
  },
  "title": "Encrypted Media Extensions HDCP Version Registry",
  "source": "w3c",
  "shortTitle": "Encrypted Media Extensions HDCP Version Registry",
  "categories": [
    "browser"
  ],
  "standing": "good"
}
```
</details>

### Tests
These changes look good! 😎

Co-authored-by: browser-specs-bot <>
Co-authored-by: François Daoust <fd@w3.org>

specs.json

@@ -1124,6 +1124,12 @@
  ]
  },
  "https://www.w3.org/TR/edit-context/",
+ {
+ "nightly": {
+ "sourcePath": "hdcp-version-registry-respec.html"
+ },
+ "url": "https://www.w3.org/TR/eme-hdcp-version-registry/"
+ },
  {
  "url": "https://www.w3.org/TR/encrypted-media-2/",
  "nightly": {