Fixes MetalCrossGL codegen removing @

[Thirulogeswaren]

changes removes the @ from variable names when converting metal to crossgl

    // Structs
    struct VertexInput {
        vec3 position @Position;
    }

    // Structs
    struct VertexOutput {
        vec4 position @gl_Position;
        vec2 uv ;
    }

after changes:

    // Structs
    struct VertexInput {
        vec3 position Position;
    }

    // Structs
    struct VertexOutput {
        vec4 position gl_Position;
        vec2 uv ;
    }