Closes #52879

## Summary

VS Code binds `Ctrl+R` to open recent workspaces/folders on all
platforms (Windows, macOS, and Linux). Zed already had this binding in
`default-windows.json`, but it was missing from `default-macos.json` and
`default-linux.json`.

Since `BaseKeymap::VSCode` returns no supplemental keymap file and
relies entirely on the platform default keymaps, users who selected VS
Code keybindings on macOS or Linux would not get the expected `Ctrl+R`
behavior — instead getting nothing, or having to use the non-VSCode
binding (`Alt+Cmd+O` / `Alt+Ctrl+O`).

This adds the missing binding to both platform defaults, consistent with
what Windows already had.

## Screenshot
The default keybinding in VS Code:
<img width="1512" height="319" alt="Screenshot 2026-04-01 at 07 38 09"
src="https://github.com/user-attachments/assets/12d483a3-3c52-4649-a00f-ee2b8e40bc8c"
/>


Release Notes:

- Added `Ctrl+R` keybinding for opening recent projects on macOS and
Linux, matching VS Code's default behavior on all platforms.