Better/complete documentation of sys.stdin/stdout/stderr default behavior

See https://docs.python.org/3/library/sys.html?highlight=stdin#sys.stdin
The default behavior of sys.stdin/stdout/stderr is not fully documented (e.g. the default newline mode, depending on OS), and the current existing documentation is a lot more difficult to understand than it would need to be, referring to internal c-api settings instead of explaining in clear language what is going.

Given how important this information is and given that the behavior of sys.stdin/out/err is surprisingly DIFFERENT from what the default would be if open with default settings would be used, making the documentation more complete and easier to understand would be rather important. The number of questions on stackoverlow (partly with incorrect or hard to verify answers) about this is a good indicator of how confusing and important this matter is.

Inizia dalla sezione relativa a sys.stdin, sys.stdout e sys.stderr nella pagina collegata della documentazione di Python, quindi confronta la descrizione con il comportamento di open usando le impostazioni predefinite nei diversi sistemi operativi. Il lavoro è completo quando il comportamento predefinito dei caratteri di nuova riga e le altre differenze rilevanti sono spiegati in modo chiaro e accurato senza ricorrere alla terminologia interna della C API.