Bind ctrl-w to DeleteToPreviousWordStart (#8606)

Even though I use Vim mode, I'd love to have this in the command
palette/fuzzy finder. It's an Emacs keybinding, but also supported by
macOS nearly everywhere.

Release Notes:

- N/A

assets/keymaps/default-macos.json

@@ -49,6 +49,7 @@
       "cmd-backspace": "editor::DeleteToBeginningOfLine",
       "cmd-delete": "editor::DeleteToEndOfLine",
       "alt-backspace": "editor::DeleteToPreviousWordStart",
+      "ctrl-w": "editor::DeleteToPreviousWordStart",
       "alt-delete": "editor::DeleteToNextWordEnd",
       "alt-h": "editor::DeleteToPreviousWordStart",
       "alt-d": "editor::DeleteToNextWordEnd",