Starting in Xcode 15, the simulator is no longer included in Xcode and must be downloaded and installed separately.

If you try to run flutter and the simulator is missing, you'll get an error like
```
xcodebuild: error: Unable to find a destination matching the provided destination specifier:
               		{ id:B1234A5C-67B8-901D-B2CB-FE34F56BDE78 }

               	Ineligible destinations for the "Runner" scheme:
               		{ platform:iOS, id:dvtdevice-DVTiPhonePlaceholder-iphoneos:placeholder, name:Any iOS Device, error:iOS 17.0 is not installed. To use with Xcode, first download and install the platform }
```

Print a pretty error to make it easier for developers to know what to do.

Part 2 of https://github.com/flutter/flutter/issues/129558.