Helix Select Mode (#37748)

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.

---------

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

assets/keymaps/vim.json

@@ -325,6 +325,27 @@
       "\"": "vim::PushRegister"
     }
   },
+  {
+    "context": "vim_mode == helix_select",
+    "bindings": {
+      "escape": "vim::NormalBefore",
+      ";": "vim::HelixCollapseSelection",
+      "~": "vim::ChangeCase",
+      "ctrl-a": "vim::Increment",
+      "ctrl-x": "vim::Decrement",
+      "shift-j": "vim::JoinLines",
+      "i": "vim::InsertBefore",
+      "a": "vim::InsertAfter",
+      "p": "vim::Paste",
+      "u": "vim::Undo",
+      "r": "vim::PushReplace",
+      "s": "vim::Substitute",
+      "ctrl-pageup": "pane::ActivatePreviousItem",
+      "ctrl-pagedown": "pane::ActivateNextItem",
+      ".": "vim::Repeat",
+      "alt-.": "vim::RepeatFind"
+    }
+  },
   {
     "context": "vim_mode == insert",
     "bindings": {
@@ -396,7 +417,12 @@
     "bindings": {
       "i": "vim::HelixInsert",
       "a": "vim::HelixAppend",
-      "ctrl-[": "editor::Cancel",
+      "ctrl-[": "editor::Cancel"
+    }
+  },
+  {
+    "context": "(vim_mode == helix_normal || vim_mode == helix_select) && !menu",
+    "bindings": {
       ";": "vim::HelixCollapseSelection",
       ":": "command_palette::Toggle",
       "m": "vim::PushHelixMatch",