SPIRV-Reflect incorrectly reports padded_size for members of a storage block

Given the following shader I think SPIRV-Reflect does not properly report `padded_size` for the members of SBO:

```
struct S
{
float aa;
float bb;
};

layout(binding = 0, std140) buffer SBO
{
S s1[2][3];
S s2;
} sbo;

void main()
{
gl_Position = vec4(sbo.s1[0][0].aa, 0, 0, 0);
}
```

I get 4 for both `aa` and `bb`, which makes it impossible to correctly compute offsets for members of SBO. In a full reflection of `SBO` I'd expect to get the following offsets:

```
s1[0][0].aa -> 0
s1[0][0].bb -> 4
s1[0][1].aa -> 16
s1[0][1].bb -> 20
s1[0][2].aa -> 32
s1[0][2].bb -> 36
s1[1][0].aa -> 48
s1[1][0].bb -> 52
s1[1][1].aa -> 64
s1[1][1].bb -> 68
s1[1][2].aa -> 80
s1[1][2].bb -> 84
s2.aa -> 96
s2.bb -> 100
```

Instead what I see is this:

```
s1[0][0].aa -> 0
s1[0][0].bb -> 4
s1[0][1].aa -> 8
s1[0][1].bb -> 12
s1[0][2].aa -> 16
s1[0][2].bb -> 20
s1[1][0].aa -> 24
s1[1][0].bb -> 28
s1[1][1].aa -> 32
s1[1][1].bb -> 36
s1[1][2].aa -> 40
s1[1][2].bb -> 44
s2.aa -> 48
s2.bb -> 52
```

Interestingly this works fine for uniform blocks, i.e. if I replace `buffer` with `uniform` in my example, `padded_size` gets reported correctly.

Start with the shader reproducer in the issue and compare reflection of the std140 storage block with the uniform-block variant, focusing on how nested array members contribute to padded_size. Done means the storage-block offsets match the listed expected offsets for s1 and s2, while the existing uniform-block behavior remains correct.

Written by the indexing model from the issue text.