Also adds tests for finding declaration of arrays inside
CppComprehension which requires proper parsing for passing.
Side-effect of this patch: if we ctrl+click on array variables, it
should jump to the correct declaration inside HackStudio.
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.