New Feature: Add support for shader imports

Hi 👋

Apologies if this is already supported and I missed it!
Do you think it would be worth adding support for shader code imports?

I’m happy to do it with some support on getting it with the right structure.

In my project I:

Created a folder in src/glsl for the shaders.
Currently each effect is a subfolder and includes the vertex and fragment shaders if necessary (e.g. src/glsl/effect/vertex.glsl).

Added this to the webpack.common.js config:

{
  test: /\.(glsl|vs|fs)$/,
  loader: 'ts-shader-loader',
  exclude: /node_modules/,
},

Still had to add the glsl.d.ts file to the src/glsl folder, containing:

declare module '*.glsl' {
  const value: string;
  export default value;
}

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Let me know what you think

[DiogoNeves]

I thank you for letting me contribute 😅 glad it was ok

[RaananW]

Thanks again 😃