### Godot version

4.0.2.stable

### System information

Windows 11, Vulkan, RTX2070 Super

### Issue description

Reading from `VIEWPORT_SIZE` in the `light()` function causes spatial shader to break and renders as default white.

### Steps to reproduce

![image](https://user-images.githubusercontent.com/20043270/236914345-ccd12e83-4431-4a53-b67b-028c8ef5719b.png)

when line 51 is present the fails to compile with the following message in the output log but no compilation errors.

```
servers/rendering/renderer_rd/forward_clustered/scene_shader_forward_clustered.cpp:171 - Condition "!shader_singleton->shader.version_is_valid(version)" is true.
  drivers/vulkan/rendering_device_vulkan.cpp:5361 - Condition "!shader" is true. Returning: RID()
  drivers/vulkan/rendering_device_vulkan.cpp:5835 - Condition "!us" is true.
```

commenting out line 51 solves this issue.

[The documentation](https://docs.godotengine.org/en/stable/tutorials/shaders/shader_reference/spatial_shader.html#light-built-ins) states that `VIEWPORT_SIZE` should be available to the `light()` function.

### Minimal reproduction project

N/A
singleton = this;
}
void SceneShaderForwardMobile::init(const String p_defines) {
	RendererRD::MaterialStorage *material_storage = RendererRD::MaterialStorage::get_singleton();
	
	{
		Vector<String> shader_versions;
		shader_versions.push_back(""); 
		shader_versions.push_back("\n#define USE_LIGHTMAP\n"); 
		shader_versions.push_back("\n#define MODE_RENDER_DEPTH\n"); 
		shader_versions.push_back("\n#define MODE_RENDER_DEPTH\n#define MODE_DUAL_PARABOLOID\n"); 
		shader_versions.push_back("\n#define MODE_RENDER_DEPTH\n#define MODE_RENDER_MATERIAL\n"); 
		
		shader_versions.push_back("\n#define USE_MULTIVIEW\n"); 
		shader_versions.push_back("\n#define USE_MULTIVIEW\n#define USE_LIGHTMAP\n"); 
		shader_versions.push_back("\n#define USE_MULTIVIEW\n#define MODE_RENDER_DEPTH\n"); 
		shader.initialize(shader_versions, p_defines);
		if (!RendererCompositorRD::get_singleton()->is_xr_enabled()) {
			shader.set_variant_enabled(SHADER_VERSION_COLOR_PASS_MULTIVIEW, false);
			shader.set_variant_enabled(SHADER_VERSION_LIGHTMAP_COLOR_PASS_MULTIVIEW, false);
			shader.set_variant_enabled(SHADER_VERSION_SHADOW_PASS_MULTIVIEW, false);
		}
	}
	material_storage->shader_set_data_request_function(RendererRD::MaterialStorage::SHADER_TYPE_3D, _create_shader_funcs);
	material_storage->material_set_data_request_function(RendererRD::MaterialStorage::SHADER_TYPE_3D, _create_material_funcs);
	{
		
		ShaderCompiler::DefaultIdentifierActions actions;
		actions.renames["MODEL_MATRIX"] = "read_model_matrix";