[3.13] gh-151623: Improve curses documentation and docstrings (GH-151625) (GH-151629...

[3.13] gh-151623: Improve curses documentation and docstrings (GH-151625) (GH-151629) (GH-151630)

(cherry picked from commit 015cc42bc254dd1fbfcb799869cb6e8196fd1c84)

Fix errors and clarify the curses, curses.panel and curses.ascii docs
against X/Open Curses and ncurses, and sync the affected docstrings.
(cherry picked from commit 65afcdd8dfb3621ac696fce076e6282c76a04b2b)