We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
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.
The ToDoEntries and ToDoEntriesWidget classes now have methods for
clearing the entries, before entries would stay permanently, even after
switching to a new project.
