shader: parse vertex metadata once when a shader is mapped

src/graphics/shader/shaderVertexMetadata.h

@@ -4,7 +4,6 @@
 #include "graphics/shader/shader.h"
 
 #include <span>
-#include <string>
 
 namespace Libs::Graphics {
 
@@ -14,9 +13,10 @@ struct ShaderVertexMetadata {
 	std::span<const ShaderSemantic> input_semantics;
 };
 
-// Validates the vertex metadata and returns a view into the shader header.
-bool ShaderReadVertexMetadata(const ShaderMappedData& data, uint32_t max_user_sgprs,
-                              ShaderVertexMetadata& metadata, std::string* error);
+// Reads the vertex metadata as a view into the shader header. Returns nullptr if it is
+// valid, otherwise why it was rejected.
+const char* ShaderReadVertexMetadata(const ShaderMappedData& data, uint32_t max_user_sgprs,
+                                     ShaderVertexMetadata& metadata);
 
 } // namespace Libs::Graphics