Add option to use utf-16 positions instead of utf-8

We use this parser for a custom linter that we ship through a VSCode extension (rustpython_parser::ast::Suite::parse_without_path). The VSCode extension api expects byte positions to the text encoded in utf-16, but the parser returns the byte positions to text encoded in utf-8. Can we add an option to use utf-16 encoded byte positions?

I'd be happy to implement this feature if you're comfortable with adding it to the parser. Do you have suggestions on how the API should look like?

從 rustpython_parser::ast::Suite::parse_without_path 開始，追蹤原始碼位置如何產生及公開。檢視現有的 parser API 與位置相關的測試，然後確定一種用於選取 UTF-16 位置的 API 形式。完成的標準是該選項已實作，且其位置行為已由測試涵蓋。