vim: subword motions (#8725)

Add subword motions to vim, inspired by
[nvim-spider](https://github.com/chrisgrieser/nvim-spider),
[CamelCaseMotion](https://github.com/bkad/CamelCaseMotion).


Release Notes:

- Added subword motions to vim

docs/src/configuring_zed__configuring_vim.md

@@ -88,6 +88,22 @@ You can see the bindings that are enabled by default in vim mode [here](https://
 
 The details of the context are a little out of scope for this doc, but suffice to say that `menu` is true when a menu is open (e.g. the completions menu), `VimWaiting` is true after you type `f` or `t` when we’re waiting for a new key (and you probably don’t want bindings to happen). Please reach out on [GitHub](https://github.com/zed-industries/zed) if you want help making a key bindings work.
 
+## Subword motion
+
+Subword motion is not enabled by default. To enable it, add these bindings to your keymap.
+
+```json
+  {
+    "context": "Editor && VimControl && !VimWaiting && !menu",
+    "bindings": {
+      "w": "vim::NextSubwordStart",
+      "b": "vim::PreviousSubwordStart",
+      "e": "vim::NextSubwordEnd",
+      "g e": "vim::PreviousSubwordEnd"
+    }
+  },
+```
+
 ## Command palette
 
 Vim mode allows you to enable Zed’s command palette with `:`. This means that you can use vim's command palette to run any action that Zed supports.