[SPARK-35398][SQL] Simplify the way to get classes from ClassBodyEvaluator in CodeGenerator.updateAndGetCompilationStats method

### What changes were proposed in this pull request?
SPARK-35253 upgraded janino from 3.0.16 to 3.1.4, `ClassBodyEvaluator` provides the `getBytecodes` method to get
the mapping from `ClassFile#getThisClassName` to `ClassFile#toByteArray` directly in this version and we don't need to get this variable by reflection api anymore.

So the main purpose of this pr is simplify the way to get `bytecodes` from `ClassBodyEvaluator` in `CodeGenerator#updateAndGetCompilationStats` method.

### Why are the changes needed?
Code simplification.

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?

- Pass the Jenkins or GitHub Action

- Manual test:

1. Define a code fragment to be tested, for example:
```
    val codeBody = s"""
        public java.lang.Object generate(Object[] references) {
          return new TestMetricCode(references);
        }

        class TestMetricCode {

          public TestMetricCode(Object[] references) {
          }

          public long sumOfSquares(long left, long right) {
            return left * left + right * right;
          }
        }
      """
```
2. Create a `ClassBodyEvaluator` and `cook` the `codeBody` as above, the process of creating `ClassBodyEvaluator` can extract from `CodeGenerator#doCompile` method.

3. Get `bytecodes` using `ClassBodyEvaluator#getBytecodes` api(after this pr) and reflection api(before this pr) respectively, then assert that they are the same. If the `bytecodes` not changed, we can be sure that metrics state will not change. The test code example as follows:
```
    import scala.collection.JavaConverters._
    val bytecodesFromApi = evaluator.getBytecodes.asScala
    val bytecodesFromReflectionApi = {
      val scField = classOf[ClassBodyEvaluator].getDeclaredField("sc")
      scField.setAccessible(true)
      val compiler = scField.get(evaluator).asInstanceOf[SimpleCompiler]
      val loader = compiler.getClassLoader.asInstanceOf[ByteArrayClassLoader]
      val classesField = loader.getClass.getDeclaredField("classes")
      classesField.setAccessible(true)
      classesField.get(loader).asInstanceOf[java.util.Map[String, Array[Byte]]].asScala
    }

    assert(bytecodesFromApi == bytecodesFromReflectionApi)
```

Closes #32536 from LuciferYang/SPARK-35253-FOLLOWUP.

Authored-by: yangjie01 <[email protected]>
Signed-off-by: Takeshi Yamamuro <[email protected]>

Author: LuciferYang

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/CodeGenerator.scala

@@ -18,7 +18,6 @@
 package org.apache.spark.sql.catalyst.expressions.codegen
 
 import java.io.ByteArrayInputStream
-import java.util.{Map => JavaMap}
 
 import scala.collection.JavaConverters._
 import scala.collection.mutable
@@ -28,8 +27,7 @@ import scala.util.control.NonFatal
 import com.google.common.cache.{CacheBuilder, CacheLoader}
 import com.google.common.util.concurrent.{ExecutionError, UncheckedExecutionException}
 import org.codehaus.commons.compiler.{CompileException, InternalCompilerException}
-import org.codehaus.commons.compiler.util.reflect.ByteArrayClassLoader
-import org.codehaus.janino.{ClassBodyEvaluator, SimpleCompiler}
+import org.codehaus.janino.ClassBodyEvaluator
 import org.codehaus.janino.util.ClassFile
 
 import org.apache.spark.{TaskContext, TaskKilledException}
@@ -1434,15 +1432,7 @@ object CodeGenerator extends Logging {
    */
   private def updateAndGetCompilationStats(evaluator: ClassBodyEvaluator): ByteCodeStats = {
     // First retrieve the generated classes.
-    val classes = {
-      val scField = classOf[ClassBodyEvaluator].getDeclaredField("sc")
-      scField.setAccessible(true)
-      val compiler = scField.get(evaluator).asInstanceOf[SimpleCompiler]
-      val loader = compiler.getClassLoader.asInstanceOf[ByteArrayClassLoader]
-      val classesField = loader.getClass.getDeclaredField("classes")
-      classesField.setAccessible(true)
-      classesField.get(loader).asInstanceOf[JavaMap[String, Array[Byte]]].asScala
-    }
+    val classes = evaluator.getBytecodes.asScala
 
     // Then walk the classes to get at the method bytecode.
     val codeAttr = Utils.classForName("org.codehaus.janino.util.ClassFile$CodeAttribute")