feat: Add button to select mobile emulator before launching

### Problem

In the "+" menu, the "Launch mobile emulator" button launches a pre-selected default emulator. If I want a different device, I have to wait for the default to finish booting, fully close it, then launch the one I actually wanted. Closing an emulator cleanly takes time, in my experience.

### Solution

Add a new option in the "+" menu that opens a device picker before launching, instead of going straight to the default.