Add XML documentation for Java.Lang.Invoke

The `Java.Lang.Invoke` namespace contains **430** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

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

## Update log

- 2026-09-10: Refreshed the placeholder scan from **496** to **430** (reduced by **66**). Related documentation PRs: [#408](https://github.com/dotnet/android-api-docs/pull/408), [#441](https://github.com/dotnet/android-api-docs/pull/441), [#476](https://github.com/dotnet/android-api-docs/pull/476), [#500](https://github.com/dotnet/android-api-docs/pull/500), [#552](https://github.com/dotnet/android-api-docs/pull/552), [#644](https://github.com/dotnet/android-api-docs/pull/644).

Start by running the provided rg command from the repository root to inspect the 430 remaining placeholders under docs\xml for Java.Lang.Invoke, excluding docs\xml\index.xml. Read the matching ns-Java.Lang.Invoke.xml and Java.Lang.Invoke/** entries to understand the affected API members. Done means the namespace's 430 reported "To be added" placeholders have useful XML documentation and the scan no longer reports them.

Vom Indexierungsmodell aus dem Issue-Text verfasst.