Fully load all shaders to prevent future performance hiccups.

Usually graphics drivers do not actually prepare shaders until they are first needed. However when some object is first rendered with a previously unused shader, there can be a hiccup because the driver is compiling/optimizing the shader. This can be quite noticeable on mobile platforms.

Calling this function will perform dummy one-invisible-triangle rendering with all permutations of all currently loaded shaders. This can take some time but helps to avoid hiccups in the future.

Please be aware that this function will only warmup shaders that are currently loaded. If you use Resources.Load to load shaders, you will need to call WarmupAllShaders again. Also, different fog modes are implemented through shader patching, so if you change fog mode at runtime, you need to do so before calling WarmupAllShaders.