This method initializes the table function context for the first time with the serialized size of tblCtxObj.
A UDF can use the table function context as a scratchpad to retain data between iterations of a local table function copy.
If tblCtxObj has object type fields, the UDF must initialize those fields to non-null values before calling allocCtx(). If tblCtxObj has array type fields, the UDF must initialize the array itself and each element of the array to a non-null value before calling allocCtx().
The maximum size of tblCtxObj is 64 KB.