internal/graphicsdriver/opengl: precompile Kage to GLSL for bulitin shaders

[hajimehoshi]

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What feature would you like to be added?

Compiling Kage to GLSL shader takes a little cost.

So, what about precompiling bulitin Kage shaders to GLSL? Unfortunately we cannot precompile GLSL to a binary form, so if we do, we prepare a GLSL source.

This is similar to #2984.

Why is this needed?

No response

[hajimehoshi]

From #3078, getProgramParameter takes much longer than compiling shaders. Precompiling Kage shader is a little risky as fixing the shader parser might not be reflected to the precompiled shaders accidentally.

Let's revisit this later.