It is a regression after https://github.com/JetBrains/skiko/pull/811

After that PR, OpenGL functions are linked in runtime via function `loadOpenGLLibrary`. We didn't call it in `makeGL` functions. Now we call.

Adding also `isLoaded` to avoid loading it multiple times

Fixes https://youtrack.jetbrains.com/issue/COMPOSE-642/Fix-Skiko-API-regression-for-creating-OpenGL-context