Add XML documentation for Android.Ranging

The `Android.Ranging` namespace contains **393** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

Example command:

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

## Update log

- 2026-09-10: Refreshed the placeholder scan from **386** to **393** (increased by **7**). Related documentation PRs: [#603](https://github.com/dotnet/android-api-docs/pull/603), [#644](https://github.com/dotnet/android-api-docs/pull/644).

Start by running the provided ripgrep command against docs\xml to inspect the 393 `To be added` placeholders under Android.Ranging and ns-Android.Ranging.xml. Review the surrounding XML documentation and existing related documentation PRs for context. The work is done when the placeholders in this namespace are replaced, excluding docs\xml\index.xml, and the scan no longer finds them.

Written by the indexing model from the issue text.