[JAVA] Vector should avoid reallocating validity buffer when necessary

Vector always reallocates validity buffer in the case of all-null or non-null

Ideally we should only allocate if the source was not provided

**Reporter**: [Zhenyuan Zhao](https://issues.apache.org/jira/browse/ARROW-3222) / @zzhao0

_{**Note**: *This issue was originally created as [ARROW-3222](https://issues.apache.org/jira/browse/ARROW-3222). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

从 BaseFixedWidthVector.java#L511 和 BitVectorHelper.java#L180 的分配路径开始，然后跟踪全为 null 的向量和非 null 向量的 validity 缓冲区是如何处理的。当且仅当未提供源时才进行分配，同时避免不必要的 validity 缓冲区重新分配后，此更改即完成。

由索引模型根据 Issue 内容生成。