[FEA] support json to struct function

[nvliyuan]

I wish we can support json to struct function:

import pyspark.sql.functions as fn
from pyspark.sql.types import *

input_data = [
  (0, """{"c1": "0", "c2": "ccc", "c3": "xxxx", "c4": "xx"}"""),
  (1, """{"c1": "0", "c2": "cccc", "c3": "xxxx", "c4": "xx"}""")
]

myDF = spark.createDataFrame(input_data, ["id", "myjson"])

myDF.write.parquet("file:/yourpath/testjson")
myDF2 = spark.read.parquet("file:/yourpath/testjson")

schema = StructType([
    StructField("c1", StringType(), True),
    StructField("c2", StringType(), True),
    StructField("c3", StringType(), True),
    StructField("c4", StringType(), True),
])

myDF2.select(fn.from_json(fn.col("myjson").cast("string"),schema)).show()