Include xcodes tool in macOS images

[allenhumphreys]

xcodes is a very handy tool for managing which version of Xcode is used in builds. While it can be used to install specific versions if they are missing, it can also be used to discover and select Xcode versions without worrying about specific naming details. Fastlane has a corresponding xcodes action that leverages the tool. Currently, we have to install xcodes as part of each job that requires xcodes to be installed to correctly select the version our build needs. This tool makes it easier to do a matrix of builds whilst preparing to migrate to the next version of Xcode.