How can I get offset from cursor using exposed function?

I found `cursor_to_offset` function internally used.
I know that I can define cursor myself, but I think there has to be a way to deal with predefined cursor. But there are not exposed.
And I'm using `graphene` actually, not `graphql_relay` directly. I think that they both don't offer such way neither.

Start by inspecting the internally used cursor_to_offset function and how predefined cursors are handled in graphql-relay-py. Check how the library is consumed through graphene and determine the public API needed to access the offset; done means callers can obtain an offset without defining a cursor themselves.

由索引模型根据 Issue 内容生成。