Add Ref images for osx

TestProjects/ShaderGraph/ProjectSettings/EditorBuildSettings.asset

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TestProjects/ShaderGraph/Assets/ReferenceImages/Linear/OSXEditor.meta

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TestProjects/ShaderGraph/Assets/ReferenceImages/Linear/OSXEditor/Metal.meta

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TestProjects/ShaderGraph/Assets/ReferenceImages/Linear/OSXEditor/Metal/MathNodes.png.meta

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