Implement gl.DrawWaterReflections

[jacobguenther]

For 2533

Implement a function gl.DrawWaterReflections which is available to unsynced lua. It essentially replicates how IWater::DrawReflections and CBumpWater::DrawReflection create reflections. It expects the caller to setup an fbo before calling it.

I have a minimal example widget here showing how to use it and for testing.

[jacobguenther]

It might be better to expose the water reflection texture as $water_reflection/LUATEX_WATER_REFLECTION. And then add a function to enable/disable generating it gl.EnableWaterReflectionTexture(boolean/options...)? But then in the unlikely event that multiple widgets/gadgets want to use it they would be stepping on each other's settings.

[jacobguenther]

Or if anybody has ideas on how to achieve the same effect with what is already available I am all ears