[FEA] Support concatenating ArrayType columns

[Dooyoung-Hwang]

I request a feature of concatenating columns of ArrayType into one column on GPU.

• Test code

data = [(1,[0.1, 0.4], [0.1, 0.4], 1.0, -1.0), (2,  [0.3, 0.5], [0.3, 0.5], 2.0, -1.0), (3, [0.3, 0.5], [2.1, 2.2], 3.0, -1.0)]
schema = StructType([ \
    StructField("a",IntegerType(),True), \
    StructField("b",ArrayType(FloatType()),True), \
    StructField("c",ArrayType(FloatType()), True), \
    StructField("d",FloatType(),True), \
    StructField("e",FloatType(),True)
  ])

df1 = spark.createDataFrame(data=data,schema=schema).withColumn("arr1", concat("b", "c"))
print(df1._jdf.queryExecution())

• Output log from spark-driver

!Expression concat(b#7221, c#7222) cannot run on GPU because expression Concat concat(b#7221, c#7222) produces an unsupported type ArrayType(FloatType,true); expression AttributeReference b#7221 produces an unsupported type ArrayType(FloatType,true); expression AttributeReference c#7222 produces an unsupported type ArrayType(FloatType,true)

[revans2]

I filed rapidsai/cudf#7767 for this.