Add XML documentation for Javax.Microedition.Khronos.Egl

The `Javax.Microedition.Khronos.Egl` namespace contains **309** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

```powershell
rg -n -i --glob 'Javax.Microedition.Khronos.Egl/**' --glob 'ns-Javax.Microedition.Khronos.Egl.xml' 'to be added' docs\xml
```

## Update log

- 2026-09-10: Refreshed the placeholder scan from **329** to **309** (reduced by **20**). Related documentation PRs: [#521](https://github.com/dotnet/android-api-docs/pull/521), [#644](https://github.com/dotnet/android-api-docs/pull/644).

Run the provided rg command against docs\xml to enumerate the 309 placeholders in the Javax.Microedition.Khronos.Egl files, excluding docs\xml\index.xml. Review the matching namespace and member XML documentation entries, then replace the placeholders with documentation. Done means the scan no longer reports those 309 entries.

由索引模型根据 Issue 内容生成。