Add XML documentation for Android.InputMethodServices

The `Android.InputMethodServices` namespace contains **323** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

Example command:

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

## Update log

- 2026-09-10: Refreshed the placeholder scan from **315** to **323** (increased by **8**). Related documentation PRs: [#644](https://github.com/dotnet/android-api-docs/pull/644).

Start with the provided rg command under docs\xml, including the Android.InputMethodServices/** files and ns-Android.InputMethodServices.xml. Review the 323 matching To be added placeholders and replace them with XML documentation; the work is done when the refreshed scan finds none in this namespace, excluding docs\xml\index.xml.

Rédigé par le modèle d'indexation à partir du texte de l'issue.