Add XML documentation for Java.Util.Zip

The `Java.Util.Zip` namespace contains **275** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

```powershell
rg -n -i --glob 'Java.Util.Zip/**' --glob 'ns-Java.Util.Zip.xml' 'to be added' docs\xml
```

## Update log

- 2026-09-10: Refreshed the placeholder scan from **278** to **275** (reduced by **3**). Related documentation PRs: [#466](https://github.com/dotnet/android-api-docs/pull/466), [#469](https://github.com/dotnet/android-api-docs/pull/469), [#471](https://github.com/dotnet/android-api-docs/pull/471), [#581](https://github.com/dotnet/android-api-docs/pull/581), [#644](https://github.com/dotnet/android-api-docs/pull/644).

Start in docs\xml by running the provided ripgrep command to inspect the 275 `To be added` placeholders under Java.Util.Zip, excluding docs\xml\index.xml. Review the affected namespace and member XML files, then replace the placeholders with documentation; done means the scan no longer reports those entries.

Written by the indexing model from the issue text.