C api for pointer types

Sometimes there is a need to check whether a type is pointer or not. For example, the only difference between a stage in/out block and a stage in/out variable of a struct type is that the block is represented as a pointer to a struct. Therefore, in order to check that a stage in/out is a block or a simple variable of a struct type, it's necessary to know whether it's a pointer type or not.

glsl:

```
1)
in InputBlock
{
float member;
} input;

2)
struct InputBlockStruct
{
float member;
}

in InputBlockStruct input;
```

Start by reviewing the existing C API and the two GLSL examples in the issue to understand how stage blocks and struct variables are represented. The work is complete when callers can determine whether a reflected type is a pointer type and distinguish these two cases through the C API.

Written by the indexing model from the issue text.