Add a static readonly Guid field to COM structs

[AArnott]

Adds a field like this to structs that represent COM interfaces:

/// <summary>The IID guid for this interface.</summary>
/// <value>{00000101-0000-0000-c000-000000000046}</value>
internal static readonly Guid Guid = new Guid(0x00000101, 0x0000, 0x0000, 0xC0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x46);

Closes #711