This moves all code comprehension-related code to a new library,
LibCodeComprehension.
This also moves some types related to code comprehension tasks (such as
autocomplete, find declaration) out of LibGUI and into
LibCodeComprehension.
This is similar to the LibJS test data that resides in
/home/anon/js-tests.
It's more convenient than storing the test programs as raw strings
in the code.