Access `TIntermediate` with public headers

### Main issue
After calling `TShader::parse()` I have been using:
```cpp
shader->getIntermediate()->getNumEntryPoints();
shader->getIntermediate()->getNumErrors();
```
when converting HLSL to SPIRV because `TShader::parse()` sometimes still succeeded in some undesirable cases. For example when entry points don't exist. So I used `getIntermediate()` to do extra checking. But that's no longer possible since the removal of some public header files.

Is there another way to do this?

### Extra question
Another thing that I wasn't yet using, but was planning to in the future is `glslang::TIntermTraverser` to do some extra application-specific code checks.
```cpp
class MyTraverser : public glslang::TIntermTraverser { ... };

auto* root = shader->getIntermediate()->getTreeRoot();
MyTraverser traverser;
root->traverse(&traverser);
```
So I would also like to know if this is something that will not be possible or if this was removed by mistake.

Start by reviewing the public-header changes affecting TShader::getIntermediate() and the TIntermTraverser entry points shown in the issue. Determine whether supported access to intermediate data and traversal should be restored or replaced; done means the API behavior and application-facing alternative are clearly defined.

Written by the indexing model from the issue text.