This patch removes the `hold` option on `alacritty_terminal` in favor of
a `drain_on_exit` option, which will drain the PTY before shutdown. The
hold logic is instead handled in `alacritty`.
Winit explicitly states that the window is not focused by default and
the `Focused` event will deliver the state later on.
Also start adding notable changes to alacritty_terminal in its own
CHANGELOG.
Closes#7866.