Unlit h/w code optimization does not work with definitions

There is an optimization to avoid emitting lighting fragments for h/w code generation

* if an "unlit" surfaceshader is defected does not work if the shader is inside a definition.
It will always omit lighting.
* Also the environment lighting information never performs any check so is always included
though unused.
* Finally for unit tests which empty out the direct lighting list, this results in a strange situation where
you emit the direct lighting code but not the maximum number of lights uniform.

Seems in part that the GLSL code has a requiresLighting() logic that is only used in one place but not others.

Example:
```xml

```

Start by tracing the GLSL requiresLighting() logic and the hardware code-generation path for surfaces inside definitions, using the XML example to compare both cases. Check how direct lighting, environment lighting, and the maximum-lights uniform are emitted, then add or run unit coverage showing that unused lighting fragments and uniforms are omitted consistently.

Written by the indexing model from the issue text.