Respect `TERM=dumb`

[9999years]

If TERM=dumb, reedline still attempts to get the cursor position, which TERM=dumb does not support.

See: https://invisible-island.net/ncurses/terminfo.src.html#tic-dumb

[fdncred]

Seems like that may be an upstream thing with crossterm. Not sure how to use this function but maybe reedline should use it?

https://github.com/crossterm-rs/crossterm/blob/4f08595ef4477de2d504dcced24060ed9e3d582a/src/ansi_support.rs#L32-L46

[playwmadness]

It seems that supports_ansi function @fdncred linked is included only in Windows builds.

Currenty in reedline, cursor::position() is used only by Painter, so I guess we can instead make painters query TERM env var on creation and if it's unset or dumb (or unknown too?), then the painter will avoid using cursor::position().

Though I noticed in GNU Readline, things like Ctrl+L change their behavior depending on the current value of TERM, so if for example you change TERM env in bash, it will instantly take it into account. So probably checking it just once isn't enough.
Maybe we should have our own wrapper for getting cursor pos, which behaves differently based on the current TERM env value.

[fdncred]

You're right about support_ansi onlyh working in Windows. I looked at that yesterday and started adding something to nushell's UseAnsiColoring functionality by checking for TERM=dumb but that doesn't help reedline. use_ansi_coloring also exists in reedline so I'm guessing that this change should be hooked up there to toggle it to false.