Provide an option to disable import ordering or customize order

I'm working on a project ([Apache Flink](https://github.com/apache/flink)) using AOSP format but with [customized import ordering](https://github.com/apache/flink/blob/e0240c782073f879a1a1e3fe22b45a38ee499c45/pom.xml#L2123-L2126). I manually set the order in `Preferences | Editor | Code Style | Java | Imports | Import Layout`, but `google-java-plugin` will override my settings when I use "Optimize Imports".

Is it possible to provide an option to disable the feature, or let users to customize the import order? Thanks!

首先檢查 google-java-format 如何處理 IDE 的 "Optimize Imports" 動作，以及 issue 中描述的 import-order 行為。確定預期實作是停用選項、可自訂排序，還是兩者兼具，然後為選定的行為定義涵蓋範圍。

由索引模型根據 Issue 內容生成。