Add Turf buffer method

还没有人认领这个 Issue。

Turf.js has a [`Turf#buffer`](http://turfjs.org/docs/#buffer) method that would be useful for defining offline map regions. An example use case in navigation would be defining a buffer around a route geometry for an offline download:


@zugaldia mentioned that this may not be a straightforward port to java, possibly necessitating bringing in a third party [library](https://github.com/locationtech/jts) to get the job done. We need to look into this a bit further / discuss if that makes sense.

cc @osana @kevinkreiser

首先检查 Turf#buffer 和关联的 LocationTech JTS 库，以了解所需的几何行为，以及是否可以从此 Java SDK 中使用它。然后确定适用于 buffer 方法的 SDK 入口点，并与维护者讨论依赖项和 API 的选择。当项目就定义带缓冲区的离线地图区域的实现路径达成一致时，即视为完成。

由索引模型根据 Issue 内容生成。