[GLSL] Invalid tess control shader is generated if fixup_clipspace is true.

When `fixup_clipspace` is enabled, spirv-cross will patch the shader with:

```
gl_Position.z = 2.0 * gl_Position.z - gl_Position.w;
```

But in TessControl shader, there is no 'gl_Position' defined. I'm also wondering whether clip-space-fixing is really desired in TessControl shader, because in most cases the outputs of this stage are not perspective-divided.

Start by tracing the `fixup_clipspace` handling for TessControl shader generation and inspect the emitted `gl_Position` use. Clarify whether clip-space fixing is intended at this stage, then ensure the generated shader is valid and its behavior matches that decision.

Written by the indexing model from the issue text.