Add Writing Assistance APIs

[browser-specs-bot]

Close #1543, adding the suggested spec to the list.

Changes to index.json

This update would trigger the following changes in index.json:

Add spec (1)

```json { "url": "https://wicg.github.io/writing-assistance-apis/", "seriesComposition": "full", "shortname": "writing-assistance-apis", "series": { "shortname": "writing-assistance-apis", "currentSpecification": "writing-assistance-apis", "title": "Writing Assistance APIs", "shortTitle": "Writing Assistance APIs", "nightlyUrl": "https://wicg.github.io/writing-assistance-apis/" }, "standing": "pending", "organization": "W3C", "groups": [ { "name": "Web Platform Incubator Community Group", "url": "https://www.w3.org/community/wicg/" } ], "nightly": { "url": "https://wicg.github.io/writing-assistance-apis/", "status": "Draft Community Group Report", "alternateUrls": [], "repository": "https://github.com/WICG/writing-assistance-apis", "sourcePath": "index.bs", "filename": "index.html" }, "title": "Writing Assistance APIs", "source": "spec", "shortTitle": "Writing Assistance APIs", "categories": [ "browser" ] } ```

Tests

These changes look good! 😎