Add XML documentation for Android.Ranging.Ble.Rssi

The `Android.Ranging.Ble.Rssi` namespace contains **47** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

Example command:

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

## Update log

- 2026-09-10: Refreshed the placeholder scan from **45** to **47** (increased by **2**). Related documentation PRs: [#644](https://github.com/dotnet/android-api-docs/pull/644).

Start by running the provided rg command against docs\xml to inspect the 47 `To be added` placeholders under Android.Ranging.Ble.Rssi and the ns-Android.Ranging.Ble.Rssi.xml file. Review the surrounding API declarations and existing documentation patterns, then confirm the scan finds no remaining placeholders in this namespace.

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