[Warp] Add a setting to define the default layout behavior when opening a file

### Pre-submit Checks - [x] I have [searched Warp feature requests](https://github.com/warpdotdev/warp/issues?q=is%3Aissue+label%3AFEATURE) and there are no duplicates - [x] I have [searched Warp docs](https://docs.warp.dev) and my feature is not there ### Describe the solution you'd like? **Current Pain Point:** Currently, the application defaults to a 50/50 split view whenever a file is opened. This automatically reorganizes the active terminal window, which disrupts existing layouts and forces the user to manually resize or move windows to regain their preferred workspace organization. **Proposed Solution:** Introduce a dropdown in the settings menu (e.g., Settings > Editor > Default Open Mode) with the following options: 1. Split View (Current): Opens the file in a 50/50 split. 2. 3. Full Window: Opens the file in a new tab or replaces the current focus without splitting. 4. 5. Background: Opens the file in a tab without switching focus from the terminal. 6. 7. Last Used: R