[SPARK-22378][SQL] Eliminate redundant null check in generated code for extracting an element from complex types
## What changes were proposed in this pull request?
This PR eliminates redundant null check in generated code for extracting an element from complex types `GetArrayItem`, `GetMapValue`, and `GetArrayStructFields`. Since these code generation does not take care of `nullable` in `DataType` such as `ArrayType`, the generated code always has `isNullAt(index)`.
This PR avoids to generate `isNullAt(index)` if `nullable` is false in `DataType`.
Example
```
val nonNullArray = Literal.create(Seq(1), ArrayType(IntegerType, false))
checkEvaluation(GetArrayItem(nonNullArray, Literal(0)), 1)
```
Before this PR
```
/* 034 */ public java.lang.Object apply(java.lang.Object _i) {
/* 035 */ InternalRow i = (InternalRow) _i;
/* 036 */
/* 037 */
/* 038 */
/* 039 */ boolean isNull = true;
/* 040 */ int value = -1;
/* 041 */
/* 042 */
/* 043 */
/* 044 */ isNull = false; // resultCode could change nullability.
/* 045 */
/* 046 */ final int index = (int) 0;
/* 047 */ if (index >= ((ArrayData) references[0]).numElements() || index < 0 || ((ArrayData) references[0]).isNullAt(index)) {
/* 048 */ isNull = true;
/* 049 */ } else {
/* 050 */ value = ((ArrayData) references[0]).getInt(index);
/* 051 */ }
/* 052 */ isNull_0 = isNull;
/* 053 */ value_0 = value;
/* 054 */
/* 055 */ // copy all the results into MutableRow
/* 056 */
/* 057 */ if (!isNull_0) {
/* 058 */ mutableRow.setInt(0, value_0);
/* 059 */ } else {
/* 060 */ mutableRow.setNullAt(0);
/* 061 */ }
/* 062 */
/* 063 */ return mutableRow;
/* 064 */ }
```
After this PR (Line 47 is changed)
```
/* 034 */ public java.lang.Object apply(java.lang.Object _i) {
/* 035 */ InternalRow i = (InternalRow) _i;
/* 036 */
/* 037 */
/* 038 */
/* 039 */ boolean isNull = true;
/* 040 */ int value = -1;
/* 041 */
/* 042 */
/* 043 */
/* 044 */ isNull = false; // resultCode could change nullability.
/* 045 */
/* 046 */ final int index = (int) 0;
/* 047 */ if (index >= ((ArrayData) references[0]).numElements() || index < 0) {
/* 048 */ isNull = true;
/* 049 */ } else {
/* 050 */ value = ((ArrayData) references[0]).getInt(index);
/* 051 */ }
/* 052 */ isNull_0 = isNull;
/* 053 */ value_0 = value;
/* 054 */
/* 055 */ // copy all the results into MutableRow
/* 056 */
/* 057 */ if (!isNull_0) {
/* 058 */ mutableRow.setInt(0, value_0);
/* 059 */ } else {
/* 060 */ mutableRow.setNullAt(0);
/* 061 */ }
/* 062 */
/* 063 */ return mutableRow;
/* 064 */ }
```
## How was this patch tested?
Added test cases into `ComplexTypeSuite`
Author: Kazuaki Ishizaki <ishizaki@jp.ibm.com>
Closes #19598 from kiszk/SPARK-22378.
3bba8621cf