Allow commas in comma separated form choices

It is a common use-case to require a comma in a form choice, such as "Please specify your income: $1,000 - $2,000" etc. I think it would be preferable to use pipe separator since it is not an English grammatical character.

While we do have a very customized form page, we are still leaning on some underpinnings of wagtail.contrib.forms, so I think we will either need to provide our own choice field, or make a contribution to wagtail to support changing it from the hard-coded comma.

首先跟踪 wagtail.contrib.forms 使用的选项解析方式，并将其与 repository 的自定义表单页面进行比较。确定可配置的管道分隔符或单独的选项字段哪一种更合适。完成的标准是：包含逗号的选项（例如 "$1,000 - $2,000"）能够被接受，而不会在逗号处分割。

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