gh-88324: Clarify documentation for redirected stdout/stderr when using subprocess in Linux

[richardhob]

The description of subprocess input parameters stdin, stdout, and stderr does not make it clear that the default behavior (==None) is "no redirection will occur". One way to make this more clear to the reader is to describe the default behavior earlier in the argument description.

Second, the statement "the child’s file handles will be inherited from the parent" is wrong, as discussed in linked issue https://bugs.python.org/issue1227748. The child file handle behavior is better described by the close_fds input argument.

Asside: close_fds description

If close_fds is true, all file descriptors except 0, 1 and 2 will be closed before the child process is executed. Otherwise when close_fds is false, file descriptors obey their inheritable flag as described in Inheritance of File Descriptors.

On Windows, if close_fds is true then no handles will be inherited by the child process unless explicitly passed in the handle_list element of STARTUPINFO.lpAttributeList, or by standard handle redirection.

Changes

1. Move the None option and description up in the documentation to make it more clear that the default behavior is "no redirection will occur"
2. Remove "the child’s file handles will be inherited from the parent." statement. The file handles are managed using the close_fds input parameter

Resolve #88324

[ghost]

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[gpshead]

thanks!