[Java] Make sure alignment and memory padding conform to spec

Per spec 8 byte alignment and padding for buffers.

**Reporter**: [Micah Kornfield](https://issues.apache.org/jira/browse/ARROW-186) / @emkornfield
#### PRs and other links:
- [GitHub Pull Request apache/arrow#98](https://github.com/apache/arrow/pull/98)

_{**Note**: *This issue was originally created as [ARROW-186](https://issues.apache.org/jira/browse/ARROW-186). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

首先检查链接的 Apache Arrow pull request #98，以及 issue 所引用的规范。检查现有 Java 缓冲区对齐和填充行为，然后验证其是否符合所需的 8 字节对齐和填充规则。

由索引模型根据 Issue 内容生成。