@Override
	public BitFieldDataType clone(DataTypeManager dtm) {
		if (dtm != getDataTypeManager()) {
			throw new AssertException("unsupported clone operation");
		}
		return this;
	}
Get the bit offset within the full base type
@return base type bit offset or -1 if unknown
Ghidra/Features/PDB/src/main/java/ghidra/app/util/bin/format/pdb/PdbBitField.java