Add XML documentation for Org.Apache.Http.Params

The `Org.Apache.Http.Params` namespace contains **119** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

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

## Update log

- 2026-09-10: Refreshed the placeholder scan from **133** to **119** (reduced by **14**). Related documentation PRs: [#426](https://github.com/dotnet/android-api-docs/pull/426), [#644](https://github.com/dotnet/android-api-docs/pull/644).

Run the provided rg command against docs\xml to enumerate the 119 placeholders under Org.Apache.Http.Params, excluding docs\xml\index.xml. Read the matching XML documentation entries and related completed documentation PRs #426 and #644 for context. Done means the namespace scan finds no remaining "To be added" placeholders.

Written by the indexing model from the issue text.