TerminalUI::suspend() is responsible for undoing all Kakoune's modifications to
the terminal state, actually suspending the process, then re-applying all the
modifications after Kakoune wakes back up.
Previously, the "undo" and "reapply" steps for termios settings were both after
the suspend point, so on some platforms they were incorrect when the user
arrived back at the shell prompt.
Now, the termios "undo" step is back before the suspend point, and the undo and
reapply steps should be in exactly reversed order.
Fixes#3488.
In terminals that support it, this sequence causes the terminal to not redraw
*its* output until the application has finished, reducing redraw flickering.
The sequence is defined in:
https://gitlab.com/gnachman/iterm2/-/wikis/synchronized-updates-spec
...and is apparently also supported by kitty and libVTE.
Fixes#3482.
insert blank seems to behave differently between terminals and would
be less efficient because it still has to shift all following characters
(that we will overwrite anyway).
Fixes#3437
Diff against known state and insert/erase relevant lines.
Erase everything first to avoid insertion invalidating lines that
get out of the terminal at bottom.
This should reduce flicker, by avoiding transient states where
info/menu windows are not displayed, and paves the way for proper
diffing of the screen.
