Implement ImageData constructors.

Source/core/html/ImageData.idl

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 [
+    Constructor(Uint8ClampedArray data, unsigned long width, [Default=Undefined] optional unsigned long height),
+    Constructor(unsigned long width, unsigned long height),
     Custom=Wrap,
+    RaisesException=Constructor,
 ] interface ImageData {
     readonly attribute long width;
     readonly attribute long height;
 };