Add XML documentation for Android.Nfc

The `Android.Nfc` namespace contains **147** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

Example command:

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

## Update log

- 2026-09-10: Refreshed the placeholder scan from **144** to **147** (increased by **3**). Related documentation PRs: [#602](https://github.com/dotnet/android-api-docs/pull/602), [#644](https://github.com/dotnet/android-api-docs/pull/644).

Run the provided rg command first to enumerate the 147 placeholders under docs\xml for Android.Nfc, excluding docs\xml\index.xml. Review the matching Android.Nfc/** and ns-Android.Nfc.xml files and the related documentation PRs #602 and #644 for conventions. Done means the Android.Nfc placeholder count is addressed and the scan confirms the intended entries no longer say “To be added”.

Written by the indexing model from the issue text.