Add XML documentation for Android.Ranging.Raw

The `Android.Ranging.Raw` namespace contains **141** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

Example command:

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

## Update log

- 2026-09-10: Refreshed the placeholder scan from **131** to **141** (increased by **10**). Related documentation PRs: [#644](https://github.com/dotnet/android-api-docs/pull/644).

Use the PowerShell rg command in the issue to enumerate the matching files under docs\xml. Read the Android.Ranging.Raw/** and ns-Android.Ranging.Raw.xml files to determine what each placeholder documents. Done means all 141 “To be added” placeholders in that namespace are replaced, excluding docs\xml\index.xml, and the scan finds none.

Scritto dal modello di indicizzazione a partire dal testo della issue.