Add explicit FLOAT32, INT32, and UINT32 to MSLShaderVariableFormat

[alexdremov]

This PR addresses failures in MoltenVK:

[mvk-error] VK_ERROR_INITIALIZATION_FAILED: Render pipeline compile failed (Error code 3):
   Fragment input(s) `user(locn10)` mismatching vertex shader output type(s) or not written by vertex shader.

MSLShaderVariableFormat previously only supported ANY32, forcing to default to UInt. This causes a Metal compiler crash (invalid return type or mismatching type) if the fragment shader actually expects a float input. By introducing explicit 32-bit types, MoltenVK can instruct SPIRV-Cross on the exact data type to use.

• Added MSL_SHADER_VARIABLE_FORMAT_FLOAT32, INT32, and UINT32 to the MSLShaderVariableFormat enum and the corresponding SPVC_MSL_SHADER_VARIABLE_FORMAT_* C-API definitions.
• Relaxed the dummy output generation condition in add_interface_block() to no longer strictly require capture_output_to_buffer. Previously, SPIRV-Cross would only generate missing interface variables if the pipeline was explicitly capturing output. This prevented MoltenVK from padding StageOut structs in standard rasterization pipelines, leading to linker failures when a Fragment shader expected an input that the Vertex shader didn't explicitly write.
• Replaced the capture_output_to_buffer requirement with get_entry_point().model != ExecutionModelFragment. This ensures that dummy output generation safely applies to all standard Vertex, Geometry, and Tessellation stages to satisfy downstream Metal linkers, while strictly preventing generic [[user(locn)]] variables from being illegally injected into the return structs of Fragment shaders.

AI use disclosure:
I am not a computer graphics expert and AI was used to help debug and prepare fixes for this issue. I confirm that I have manually tested this and a scene that was crashing before in "Detroit: Become Human" is not crashing after this fix.

[CLAassistant]

All committers have signed the CLA.

[alexdremov]

maybe is_vertex_like_shader() can be used here, I am not sure

[cdavis5e]

This seems awfully familiar...

[alexdremov]

This seems awfully familiar...

Hey! Seems like you have linked this PR. Perhaps you meant something else.