Add XML documentation for Java.Lang.Reflect

The `Java.Lang.Reflect` namespace contains **172** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

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

## Update log

- 2026-09-10: Refreshed the placeholder scan from **216** to **172** (reduced by **44**). Related documentation PRs: [#388](https://github.com/dotnet/android-api-docs/pull/388), [#470](https://github.com/dotnet/android-api-docs/pull/470), [#577](https://github.com/dotnet/android-api-docs/pull/577), [#644](https://github.com/dotnet/android-api-docs/pull/644).

Run the provided rg command to locate the 172 placeholders under docs\xml in the Java.Lang.Reflect namespace, excluding docs\xml\index.xml. Read the surrounding XML documentation entries before updating them. Done means the scan no longer reports these Java.Lang.Reflect source placeholders.

Written by the indexing model from the issue text.