keymap_ui: Add open keymap JSON button (#36182)

Closes #ISSUE

Release Notes:

- Keymap Editor: Added a button in the top left to allow opening the
keymap JSON file. Right clicking the button provides shortcuts to
opening the default Zed and Vim keymaps as well.

Cargo.lock

@@ -15054,8 +15054,10 @@ dependencies = [
  "ui",
  "ui_input",
  "util",
+ "vim",
  "workspace",
  "workspace-hack",
+ "zed_actions",
 ]
 
 [[package]]