Let's stop putting generic types and AOs from the Web IDL spec into
the Bindings namespace and directory in LibWeb, and instead follow our
usual naming rules of 'directory = namespace = spec name'. The IDL
namespace is already used by LibIDL, so Web::WebIDL seems like a good
choice.
This code generator no longer creates JS wrappers for platform objects
in the old sense, instead they're JS objects internally themselves.
Most of what we generate now are prototypes - which can be seen as
bindings for the internal C++ methods implementing getters, setters, and
methods - as well as object constructors, i.e. bindings for the internal
create_with_global_object() method.
Also tweak the naming of various CMake glue code existing around this.
