Specialization constant reflections

I have a glsl shader program with the following constants:
```glsl
layout (constant_id = 0) const int VALUE_A = 10;
layout (constant_id = 1) const float VALUE_B = 11.7f;
```
I'm trying to get these in a reflection so I can build my VkSpecializationInfo objects on the fly. I cannot find any specialization constants contained in the `glslang::TProgram` reflection.
Am I looking in the wrong spot or are the reflection of these layouts not supported yet?

Start by tracing the glslang::TProgram reflection API for the GLSL specialization-constant declarations shown in the issue. Compare its reflected data with the expected VkSpecializationInfo inputs and verify behavior using a shader containing VALUE_A and VALUE_B. Done means the reflection exposes both constants, or clearly documents that they are unsupported.

Written by the indexing model from the issue text.