Use shader-loader for shader sources

[zachmullen]

Right now they're inlined as arrays of strings with join('\n') called on them.

[manthey]

Many of the shaders are dynamically produced based on features, so are not constant strings. I don't see how shader-loader would work.

[zachmullen]

Well, there are at least some[1][2][3] that are totally static. For those cases, it would not only improve readability but also remove some unnecessary work that is being done at runtime currently.

I see some examples of dynamic shader code, such as this debug flag. Is that something that could be accomplished with preprocessor directives such that the shader program itself becomes static?

[manthey]

Resolved by #982.