Metal: last member of vertex output block is always float4 in fragment shader?

Hello.

I have an issue with one shader which has a pretty big struct used to pass data from vertex to fragment shader:
```
layout(location = 0) in VertexData
{
vec2 baseUv;
flat uvec2 albdoId;
vec3 emissiveColor;
flat float visibility;
flat uvec2 normalId;
flat float dispAmount;
flat uint materialIndex;
flat uint needsIndividualTransform;
flat mat2 baseUvFromNormalUv;
vec4 wsNormal;
vec3 wsTangent;
vec3 wsBitangent;
vec3 wsView;
} inoutData;
```

This struct gets converted to metal code in vertex shader correctly:
```
struct VertexData
{
float2 baseUv;
uint2 albdoId;
float3 emissiveColor;
float visibility;
uint2 normalId;
float dispAmount;
uint materialIndex;
uint needsIndividualTransform;
float2x2 baseUvFromNormalUv;
float4 wsNormal;
float3 wsTangent;
float3 wsBitangent;
float3 wsView;
};
```
but fragment shader has the last component type changed to float4:
```
struct VertexData
{
float2 baseUv;
uint2 albdoId;
float3 emissiveColor;
float visibility;
uint2 normalId;
float dispAmount;
uint materialIndex;
uint needsIndividualTransform;
float2x2 baseUvFromNormalUv;
float4 wsNormal;
float3 wsTangent;
float3 wsBitangent;
float4 wsView;
};
```

I have played a bit with this struct to find a workaround and it seems that the last member of the struct in fragment shader always* becomes type float4 after conversion to metal. E.g. I have added a dummy single float to keep wsView float3 and that's how generated metal looks like:
```
struct VertexData
{
float2 baseUv;
uint2 albdoId;
float3 emissiveColor;
float visibility;
uint2 normalId;
float dispAmount;
uint materialIndex;
uint needsIndividualTransform;
float2x2 baseUvFromNormalUv;
float4 wsNormal;
float3 wsTangent;
float3 wsBitangent;
float3 wsView;
float4 dummy;
};
```

Looks like a bug to me.

Thank you for the great job!

Start from the shader struct shown in the issue and reproduce its vertex-to-fragment conversion to Metal, comparing the generated structures. Trace the conversion path that handles the final member and consider the issue resolved when a final float3 member remains float3 without requiring a dummy field.

Written by the indexing model from the issue text.