Add XML documentation for Android.Gestures

The `Android.Gestures` namespace contains **220** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

Example command:

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

## Update log

- 2026-09-10: Refreshed the placeholder scan from **218** to **220** (increased by **2**). Related documentation PRs: [#644](https://github.com/dotnet/android-api-docs/pull/644).

Run the provided rg command against docs\xml to enumerate the 220 placeholders under Android.Gestures/** and ns-Android.Gestures.xml. Read each matching XML entry and replace its “To be added” text with the relevant API documentation; done means the scan returns no remaining placeholders in that scope.

Scritto dal modello di indicizzazione a partire dal testo della issue.