Add PDF Accessibility API Mappings 1.0 (#2218)

Close #1556, 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://w3c.github.io/pdf-aam/",
  "seriesComposition": "full",
  "shortname": "pdf-aam",
  "series": {
    "shortname": "pdf-aam",
    "currentSpecification": "pdf-aam",
    "title": "PDF Accessibility API Mappings",
    "shortTitle": "PDF Accessibility API Mappings",
    "nightlyUrl": "https://w3c.github.io/pdf-aam/"
  },
  "categories": [],
  "organization": "W3C",
  "groups": [
    {
      "name": "Accessible Rich Internet Applications Working Group",
      "url": "https://www.w3.org/WAI/about/groups/ariawg/"
    },
    {
      "name": "SVG Accessibility Task Force",
      "url": "https://www.w3.org/WAI/PF/svg-a11y-tf/"
    }
  ],
  "nightly": {
    "url": "https://w3c.github.io/pdf-aam/",
    "status": "Editor's Draft",
    "alternateUrls": [],
    "repository": "https://github.com/w3c/aria",
    "sourcePath": "pdf-aam/index.html",
    "filename": "index.html"
  },
  "title": "PDF Accessibility API Mappings 1.0",
  "source": "spec",
  "shortTitle": "PDF Accessibility API Mappings 1.0",
  "standing": "good"
}
```
</details>

### Tests
These changes look good! 😎

Co-authored-by: browser-specs-bot <>

Author: browser-specs-bot

specs.json

@@ -616,6 +616,12 @@
     }
   },
   "https://w3c.github.io/mediacapture-surface-control/",
+  {
+    "categories": [
+      "-browser"
+    ],
+    "url": "https://w3c.github.io/pdf-aam/"
+  },
   "https://w3c.github.io/permissions-registry/",
   {
     "url": "https://w3c.github.io/reporting/network-reporting.html",