Add XML documentation for Android.Views.Autofill

The `Android.Views.Autofill` namespace contains **52** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

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

## Update log

- 2026-09-10: Refreshed the placeholder scan from **107** to **52** (reduced by **55**). Related documentation PRs: [#360](https://github.com/dotnet/android-api-docs/pull/360), [#435](https://github.com/dotnet/android-api-docs/pull/435), [#494](https://github.com/dotnet/android-api-docs/pull/494), [#644](https://github.com/dotnet/android-api-docs/pull/644).

Start by running the provided rg scan under docs\xml for Android.Views.Autofill/** and ns-Android.Views.Autofill.xml, excluding docs\xml\index.xml. Read the 52 matching source XML documentation entries and the surrounding API context. Done means the placeholders in this namespace have been replaced with suitable documentation and the scan no longer reports them.

Written by the indexing model from the issue text.