Can't represent union types in typedefs

[timoxley]

Currently webidl2 reports "Unterminated operation" when encountering union types in typedefs.

For example, see this from the webgl 1.0 spec idl:

  typedef (ImageData or
           HTMLImageElement or
           HTMLCanvasElement or
           HTMLVideoElement) TexImageSource;

and these from the webgl 2.0 spec idl:

typedef (Uint32Array or sequence<GLuint>) UniformUIVSource;
...
typedef (Float32Array or sequence<GLfloat>) UniformMatrixFVSource;
...
typedef (Int32Array or sequence<GLint>) VertexAttribIVSource;
// etc

But according to the WebIDL grammar this should be valid, as a Typedef contains a Type:

[24]    Typedef → "typedef" ExtendedAttributeList Type identifier ";"

And a Type can be a SingleType or a UnionType:

[57]    Type    → SingleType 
 | UnionType TypeSuffix
...
[59]    UnionType   → "(" UnionMemberType "or" UnionMemberType UnionMemberTypes ")"

[timoxley]

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