Check if Xcode EULA was accepted

[spouliot]

Right now you can run uno-check successfully even if Xcode and associated tools are unusable because the EULA was not accepted (or the post-installation is not quite complete).

✔ Congratulations, everything looks great!

Press Enter to finish...

$ xcodebuild                                                                                                                                                  
You have not agreed to the Xcode and Apple SDKs license. You must agree to the license below in order to use Xcode.
Press enter to display the license:

This could be checked and, if needed, sudo xcodebuild -license accept can be executed.

It might be even better to run sudo xcodebuild -runFirstLaunch which will start by asking the EULA to be accepted and continue with any post-install requirement before the first launch.

ref: https://github.com/unoplatform/uno.vscode/issues/443