[Java] Remove reader index and writer index from ArrowBuf

Reader and writer index and functionality doesn't belong on a chunk of memory and is due to inheritance from ByteBuf. As part of removing ByteBuf inheritance, we should also remove reader and writer indexes from ArrowBuf functionality. It wastes heap memory for rare utility. In general, a slice can be used instead of a reader/writer index pattern.

**Reporter**: [Jacques Nadeau](https://issues.apache.org/jira/browse/ARROW-7494) / @jacques-n
#### PRs and other links:
- [GitHub Pull Request apache/arrow#6133](https://github.com/apache/arrow/pull/6133)

_{**Note**: *This issue was originally created as [ARROW-7494](https://issues.apache.org/jira/browse/ARROW-7494). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

まず ArrowBuf とその ByteBuf からの継承を読み、issue で説明されている読み取りインデックスと書き込みインデックスの機能を特定します。範囲を決める前に関連する API の使用箇所を追跡します。完了とは、ArrowBuf がそのインデックス機能を公開しなくなり、残りのバッファ動作が引き続き機能することです。

索引モデルが issue の本文から書いたものです。