Change Python eval to send directly instead of using temporary files

Change Python eval to send directly instead of using temporary files

* lisp/progmodes/python.el (python-shell-eval-setup-code): New
const for setting up eval (bug#49822).
(python-shell--encode-string): New function.
(python-shell-send-string): Use it to send commands directly
instead of writing to a temporary file.
(python-shell-send-string-no-output): Adjust sending.
(python-shell-send-file): Ditto.