Re-land Lazily initialise Xcode installation status (#10952)
Re-land Lazily initialise Xcode installation status (#10952)

This reverts commit 3e265e9e423392373a171be3d1303ebca1f4c7a4.

Rather than pre-compute Xcode install path, version, and EULA status,
compute and cache on demand.
tvolkert/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter,flutter/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,cbracken/flutter,tvolkert/flutter,turnidge/flutter,Hixie/flutter,tvolkert/flutter,tvolkert/flutter,cbracken/flutter,cbracken/flutter,cbracken/flutter,turnidge/flutter,Hixie/flutter,tvolkert/flutter,Hixie/flutter,flutter/flutter,Hixie/flutter,turnidge/flutter,cbracken/flutter,cbracken/flutter,tvolkert/flutter,turnidge/flutter,Hixie/flutter,Hixie/flutter,flutter/flutter,cbracken/flutter,flutter/flutter,tvolkert/flutter,tvolkert/flutter,Hixie/flutter,flutter/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,flutter/flutter,turnidge/flutter,tvolkert/flutter,flutter/flutter,Hixie/flutter