Unnecessary ProjectExec generated for Generate function

[xumingming]

Description

For the following test case:

  test("test explode1") {
    withTempView("t1") {
      sql(
        """select * from values (array(1)), (array(2)), (array(3)), (array(4))
          |as tbl(a)
     """.stripMargin).createOrReplaceTempView("t1")
      runQueryAndCompare(
        s"""
           |SELECT explode(a) from t1;
           |""".stripMargin) {
        checkGlutenOperatorMatch[GenerateExecTransformer]
      }
    }
  }

The input of explode is already an Attribute, while current implementation would still plug in a new ProjectExec, which seems not necessary?

Generate explode(a#122), false, [col#128]
+- Project [a#122, a#122]
   +- RewrittenNodeWall Filter (size(a#122, true) > 0)