Allow to resolve known mime type to file extension

Description

Mime type to file extension is already supported by FILEINFO_EXTENSION but it is impossible to specify the mime type :).

I expect code like:

$mimetype = 'application/zip';
$finfo = finfo_open(FILEINFO_EXTENSION);
var_dump(finfo_buffer($finfo, $mimetype, FILEINFO_EXTENSION)); // notice $mimetype is mime type not file data

to dump zip.

It should be possible to find the file magic data by iterating the magic data like in https://github.com/file/file/blob/FILE5_45/src/softmagic.c#L135, the mime/ext is defined in https://github.com/file/file/blob/FILE5_45/src/file.h#L371.

从 finfo_open 和 finfo_buffer 入口点开始，将请求的行为与 file's softmagic.c 和 file.h 中的引用进行比较。跟踪 FILEINFO_EXTENSION 当前如何解析数据，然后验证诸如 application/zip 这样的 MIME 类型输入会生成 zip，同时不改变现有行为。为新的解析路径添加或更新有针对性的测试。