Please credit @eliaperantoni, for the original PR (#34136).
Merge after (#34060) to avoid conflicts.

Closes https://github.com/zed-industries/zed/issues/33838
Closes https://github.com/zed-industries/zed/issues/33906

Release Notes:
- Helix will no longer sometimes fall out into "normal" mode, will
remain in "helix normal" (example: vv)
- Added dedicated "helix select" mode that can be targeted by
keybindings

Known issues:
- [ ] Helix motion, especially surround-add will not properly work in
visual mode, as it won't call `helix_move_cursor`. It is possible
however to respect self.mode in change_selection now.
- [ ] Some operations, such as `Ctrl+A` (increment) or `>` (indent) will
collapse selection also. I haven't found a way to avoid it.

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Co-authored-by: fantacell <ghub@giggo.de>
Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>