Consider exposing option for longer line lengths

While not Google's style, several other companies and projects prefer longer line length than 100 chars. My current team evaluated google-java-format, and the most contention issue was the line length being too short. I feel like the majority of the value of the formatter has been lost over this one point.

For programmers with wider monitors (more and more common these days), the 100 char line limit results in a lot of wasted space. The main benefits of the shorter line length seem to be for people looking at two pages of code side by side. However, this is not a frequent activity, and code is normally viewed one page width at a time.

I don't think the line length that google-java-format uses needs to be general purpose. I propose 120 as a straw-man. Popular projects, such as Spring and Netty use 120 chars. GitHub adds a horizontal scrollbar after 120 too. I think such projects would be much more amenable to using this formatter if there was a `--long-lines` option, similar to the `--aosp` option.

此 issue 未指出任何檔案、測試或進入點。首先釐清預期的長行選項，包括支援的長度與格式化行為，然後找出規定目前 100 個字元限制的 formatter 設定與測試。當該選項已完成文件化，且已涵蓋約定行為的格式化時，即表示完成。

由索引模型根據 Issue 內容生成。