[QUESTION] 如何配置 JSON.toJSONString 输出用空格代替制表符

目前使用 `JSON.toJSONString(manifestJson, JSONWriter.Feature.PrettyFormat)` 进行json字符串输出时，每行前方是制表符占位，如何能配置使用空格代替制表符，同时配置还可以指定几个空格，比如2个或4个。

Start by inspecting JSON.toJSONString and JSONWriter.Feature.PrettyFormat in the fastjson2 source and documentation. Determine whether indentation can be configured, then document or expose a way to select spaces and their width; done when a 2- or 4-space output configuration is available and covered by an existing serialization test.

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