Refactor `ModelDrawCommand` to keep track of `ShaderBuilder`

Currently `ModelDrawCommand` is a wrapper for the `DrawCommand`(s) that draw the primitives of the model. In `buildDrawCommand`:
1. The shader programs are built by the shader builder
2. The initial `DrawCommand` is made from the various render settings
3. The `DrawCommand` is passed into a `ModelDrawCommand` constructor; any derived commands are created / managed by that class

While this has been fine so far, it's been introducing some complications for when the derived commands use different shader programs. We're able to bypass this by having a `uniform` return different values for different commands (e.g. `u_silhouettePass` for the silhouette command), but this workaround may not be enough / efficient for future use cases.

The idea to refactor `ModelDrawCommand` would take steps 1 and 2 out from `buildDrawCommand`, and manage that in `ModelDrawCommand`. (Perhaps `buildDrawCommand` should be integrated into the class altogether?). Then, the class will have access to the `ShaderBuilder`, which it can then use to modify shaders for different commands.

Start by reading ModelDrawCommand and buildDrawCommand to understand how ShaderBuilder and the initial DrawCommand are currently managed. Define the refactor so ModelDrawCommand owns access to ShaderBuilder and can support derived commands with different shader programs, then verify existing command behavior remains intact.

Written by the indexing model from the issue text.