Fix StringSplit conversion failure

[Flyangz]

Describe the bug
Simple StringSplit fail to match in

auron/spark-extension-shims-spark/src/main/scala/org/apache/spark/sql/auron/ShimsImpl.scala

Line 527 in e03df75

if Seq(",", ", ", ":", ";", "#", "@", "_", "-", "\\|", "\\.").contains(pat.value) =>

because pat.value is UTF8String which can not be compared to String directly.

To Reproduce
debug this query in AuronQuerySuite

test("my test") {
    withTable("my_table") {
      sql("""
            |create table my_table using parquet as
            |select col1 from values ('a,A'), ('b,B'), ('c,C')
            |""".stripMargin)
      sql("""
            |select split(col1, ',')[0]
            |from my_table
            |""".stripMargin).show()
    }
  }

Expected behavior
Simple StringSplit can be converted to native.