Add tests for the following functions in test_capi.test_file:
* PyFile_FromFd()
* PyFile_GetLine()
* PyFile_NewStdPrinter()
* PyFile_WriteObject()
* PyFile_WriteString()
* PyObject_AsFileDescriptor()
Add Modules/_testlimitedcapi/file.c file.
Remove test_embed.StdPrinterTests which became redundant.
Victor Stinner