[Macros] Add missing test file

Author: DougGregor

test/Macros/Inputs/ColorLib.swift

@@ -0,0 +1,4 @@
+public struct MyColor: _ExpressibleByColorLiteral {
+  public init(_colorLiteralRed red: Float, green: Float, blue: Float, alpha: Float) { }
+  public init(_colorLiteralHue hue: Float, saturation: Float, value: Float) { }
+}