Emulating "Common User Access" / "normy GUI" idioms

[Ericson2314]

I am fond of of these idioms / old school app consistency. Now that may sound odd --- "just use Notepad++, vscode, etc. then!" but I do like modal editors too, and can think these two seemingly opposed things can play along.

Challenge 1: control- and shift- arrow keys

Modal editors tend not to really care about modifier + arrow keys, so the good news is there isn't much by way of conflicts. In

https://github.com/Ericson2314/nixos-configuration/blob/6a94e7ec30524ef4804c280566894c62d7bb15b6/user/helix/default.nix#L40-L51 / https://github.com/Ericson2314/nixos-configuration/blob/6a94e7ec30524ef4804c280566894c62d7bb15b6/user/helix/default.nix#L89-L103

I have a pretty nice first attempt. In particular, CUA "shift-" can be implemented by binding the extend_* version of commands in normal mode. This works for adjacent char / line / word motions, but not paragraph motions: goto_{prev,next}_paragraph (like the other goto_*) does not come in move vs extend variants. Is this something that could be fixed?

Challenge 2: more natural looking bar cursor / zero-width selection

I just wrote this up into an issue, #9216, as I had pondered it longer.