Add XML documentation for Java.Time.Temporal

The `Java.Time.Temporal` namespace contains **237** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

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

## Update log

- 2026-09-10: Refreshed the placeholder scan from **254** to **237** (reduced by **17**). Related documentation PRs: [#443](https://github.com/dotnet/android-api-docs/pull/443), [#484](https://github.com/dotnet/android-api-docs/pull/484), [#498](https://github.com/dotnet/android-api-docs/pull/498), [#644](https://github.com/dotnet/android-api-docs/pull/644).

Start with the provided rg command against docs\xml and the Java.Time.Temporal/** and ns-Java.Time.Temporal.xml paths to enumerate the 237 placeholders. Read the surrounding XML documentation entries to understand their format and source API context. Done means replacing the in-scope “To be added” placeholders with documentation while excluding docs\xml\index.xml, then rerunning the scan to verify none remain.

索引モデルが issue の本文から書いたものです。