Add XML documentation for Org.Apache.Http.Conn.Routing

The `Org.Apache.Http.Conn.Routing` namespace contains **6** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

```powershell
rg -n -i --glob 'Org.Apache.Http.Conn.Routing/**' --glob 'ns-Org.Apache.Http.Conn.Routing.xml' 'to be added' docs\xml
```

## Update log

- 2026-09-10: Refreshed the placeholder scan from **111** to **6** (reduced by **105**). Related documentation PRs: [#530](https://github.com/dotnet/android-api-docs/pull/530), [#644](https://github.com/dotnet/android-api-docs/pull/644).

Run the provided rg command in docs\xml to locate the six remaining placeholders under Org.Apache.Http.Conn.Routing. Read the matching namespace and member entries, then replace each `To be added` value with accurate XML documentation and rerun the scan to confirm no placeholders remain.

Written by the indexing model from the issue text.