Add XML documentation for Android.Bluetooth.LE

The `Android.Bluetooth.LE` namespace contains **550** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

Example command:

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

## Update log

- 2026-09-10: Refreshed the placeholder scan from **513** to **550** (increased by **37**). Related documentation PRs: [#644](https://github.com/dotnet/android-api-docs/pull/644).

Start with the provided rg command to locate the `To be added` entries under `docs\xml`, excluding `docs\xml\index.xml`. Review the matching `Android.Bluetooth.LE/**` and `ns-Android.Bluetooth.LE.xml` documentation, then replace the placeholders with the appropriate API descriptions. Done means the scan no longer finds placeholders in this namespace.

由索引模型根据 Issue 内容生成。