[SPARK-17061][SPARK-17093][SQL] MapObjects` should make copies of unsafe-backed data

## What changes were proposed in this pull request?

Currently `MapObjects` does not make copies of unsafe-backed data, leading to problems like [SPARK-17061](https://issues.apache.org/jira/browse/SPARK-17061) [SPARK-17093](https://issues.apache.org/jira/browse/SPARK-17093).

This patch makes `MapObjects` make copies of unsafe-backed data.

Generated code - prior to this patch:
```java
...
/* 295 */ if (isNull12) {
/* 296 */   convertedArray1[loopIndex1] = null;
/* 297 */ } else {
/* 298 */   convertedArray1[loopIndex1] = value12;
/* 299 */ }
...
```

Generated code - after this patch:
```java
...
/* 295 */ if (isNull12) {
/* 296 */   convertedArray1[loopIndex1] = null;
/* 297 */ } else {
/* 298 */   convertedArray1[loopIndex1] = value12 instanceof UnsafeRow? value12.copy() : value12;
/* 299 */ }
...
```

## How was this patch tested?

Add a new test case which would fail without this patch.

Author: Liwei Lin <lwlin7@gmail.com>

Closes #14698 from lw-lin/mapobjects-copy.