Updates to shader hooks for 2.0

[davepagurek]

Problems this aims to address:

• Currently, you have to multiply all color channels by the alpha channel in your shader. That's super easy to forget and confusing when it happens!
• Currently in fragment shaders, in one hook, you can adjust color based on the normal, the normal based on the color, or whatever you want, because you can modify all the inputs at once in a hook. The vertex shaders, meanwhile, force you to update position before normal before color, which means that you can't update the position based on the normal if you wanted

Changes

• Rearranges where premultiplied alpha happens in the shader so that shader writers don't have to worry about premultiplying any alpha
• Update vertex shader hooks to use an input struct like fragment shader hooks so that users can change any input based on any other input
  • Put input into structs
  • Pass in normal matrix in model + camera parts so you can choose which space to work in

Screenshots of the change:

N/A

PR Checklist

• npm run lint passes
• Inline documentation is included / updated
• Unit tests are included / updated