[FEA] Support count on Struct of Map(String,String)

[viadea]

I wish we can support count on Struct of Map(String,String).

For example:

import org.apache.spark.sql.Row
import org.apache.spark.sql.types._

val data = Seq(
    Row("Adam",Map("hair"->"black","eye"->"black"), Row("address" , Map("state"->"CA"),Map("city"->"santa clara"))),
    Row("Bob",Map("hair"->"red","eye"->"red"),Row("address", Map("state"->"GA"),Map("city"->"abc"))),
    Row("Cathy",Map("hair"->"blue","eye"->"blue"),Row("address",Map("state"->"NC"),Map("city"->"xyz")))
)

val mapType  = DataTypes.createMapType(StringType,StringType)

val schema = new StructType().add("name",StringType).add("properties", mapType).add("prop2", new StructType().add("propname",StringType).add("address", mapType).add("address2", mapType))

val mapTypeDF = spark.createDataFrame(spark.sparkContext.parallelize(data),schema)
mapTypeDF.write.format("parquet").mode("overwrite").save("/tmp/testparquet")
val df1 = spark.read.parquet("/tmp/testparquet")
df1.createOrReplaceTempView("df1")
df1.printSchema

spark.sql("SELECT count(prop2) FROM df1").collect()

Not-supported messages:

!Expression <Count> count(prop2#228) cannot run on GPU because input expression AttributeReference prop2#228 (child MapType(StringType,StringType,true) is not supported, child MapType(StringType,StringType,true) is not supported)

[sameerz]

This is a duplicate of #5060