Add XML documentation for Android.Hardware

The `Android.Hardware` namespace contains **526** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

Example command:

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

## Update log

- 2026-09-10: Refreshed the placeholder scan from **524** to **526** (increased by **2**). Related documentation PRs: [#608](https://github.com/dotnet/android-api-docs/pull/608), [#641](https://github.com/dotnet/android-api-docs/pull/641), [#644](https://github.com/dotnet/android-api-docs/pull/644).

Run the provided rg command against docs\xml to enumerate the Android.Hardware placeholders, then review the matching XML files and nearby completed entries for context. Replace the in-scope “To be added” documentation and rerun the scan; done means the 526 reported placeholders are addressed while docs\xml\index.xml remains excluded.

Written by the indexing model from the issue text.