The identifier type of the referenced object, represented as an integer.
{i} is the identifier type represented by one of the following integers:
0 = Null
1 = Imported asset
2 = Scene object
3 = Source asset
4 = Built-in asset
The identifierType constitutes the {i} element in the string representation of a GlobalObjectId, the format of which is:GlobalObjectId_V1-{i}-{a}-{l}-{p}