In the future, the GL context will be shared between zero or more views. The engine will also need to be able to make the GL context current even if the app is currently in headless mode. No tests are updated as this is a refactoring with no functionality changes. Part of https://github.com/flutter/flutter/issues/137267 [C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style