Add XML documentation for Android.Hardware.Camera2

The `Android.Hardware.Camera2` namespace contains **1,078** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

Example command:

```powershell
rg -n -i --glob 'Android.Hardware.Camera2/**' --glob 'ns-Android.Hardware.Camera2.xml' 'to be added' docs\xml
```

## Update log

- 2026-09-10: Refreshed the placeholder scan from **1,066** to **1,078** (increased by **12**). 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 1,078 placeholders under Android.Hardware.Camera2, excluding docs\xml\index.xml. Review the surrounding source XML documentation to determine the missing reference content. Done means the namespace's placeholders have been replaced with documentation and the scan no longer reports them.

Escrito por el modelo de indexación a partir del texto del issue.