Add XML documentation for Org.XmlPull.V1

The `Org.XmlPull.V1` namespace contains **174** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

```powershell
rg -n -i --glob 'Org.XmlPull.V1/**' --glob 'ns-Org.XmlPull.V1.xml' 'to be added' docs\xml
```

## Update log

- 2026-09-10: Refreshed the placeholder scan from **183** to **174** (reduced by **9**). Related documentation PRs: [#463](https://github.com/dotnet/android-api-docs/pull/463), [#635](https://github.com/dotnet/android-api-docs/pull/635), [#644](https://github.com/dotnet/android-api-docs/pull/644).

Start by running the provided `rg` command against `docs\xml` to list the remaining placeholders under `Org.XmlPull.V1/**` and `ns-Org.XmlPull.V1.xml`. Read the surrounding XML documentation for each match and replace the 174 `To be added` entries; done when the placeholder scan returns no remaining matches.

Vom Indexierungsmodell aus dem Issue-Text verfasst.