Add XML documentation for Android.Renderscripts

The `Android.Renderscripts` namespace contains **1,457** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

Example command:

```powershell
rg -n -i --glob 'Android.Renderscripts/**' --glob 'ns-Android.Renderscripts.xml' 'to be added' docs\xml
```

## Update log

- 2026-09-10: Refreshed the placeholder scan from **1,449** to **1,457** (increased by **8**). Related documentation PRs: [#644](https://github.com/dotnet/android-api-docs/pull/644).

Run the provided rg command against docs\xml to enumerate the 1,457 `To be added` placeholders under Android.Renderscripts, then inspect the matching namespace and API XML files. Replace the placeholders with appropriate Android.Renderscripts reference documentation and rerun the scan; done means no targeted placeholders remain.

Written by the indexing model from the issue text.