Add XML documentation for Android.Service.Controls.Templates

The `Android.Service.Controls.Templates` namespace contains **209** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

Example command:

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

## Update log

- 2026-09-10: Refreshed the placeholder scan from **207** to **209** (increased by **2**). Related documentation PRs: [#644](https://github.com/dotnet/android-api-docs/pull/644).

Start in docs\xml, using the provided rg command to locate the 209 'To be added' placeholders under Android.Service.Controls.Templates and excluding docs\xml\index.xml. Read the surrounding XML documentation for each entry and replace the placeholders with accurate descriptions. Done means the namespace's source XML documentation no longer contains those placeholders.

Vom Indexierungsmodell aus dem Issue-Text verfasst.