script/install-xcode is a self-contained script that installs Xcode.

Apple credentials are accepted over stdin (or prompt if none are
supplied.)  Using curl and perl's `HTML::Tree`, they are validated
against https://appleid.apple.com/.

Assuming they check out, support for assistive devices is enabled
(this requires sudo.) Using Applescript to script the UI, the App
Store is opened and Xcode is installed.

Xcode is then opened, and the CLI tools are installed.  The only hard
part of the cli tools is navigating the administrator password prompt
you get when you press the install button.

This is the same as your sudo password, but rather than explicitly
carry that around we just turn the password check off (by patching
/etc/authorization in a certain way.)

This is incomplete, since it does not yet handle first-time Xcode
start up tasks, such as accepting the license.