This patch lets us view the size information when inspecting type
aliases. E.g. for C++ code like the following, we'll now see the
size (8) and alignment (also 8) when hovering Bar. Previously,
that was only shown when hovering Foo:

struct Foo { double m; };
using Bar = Foo;

Sadly, this patch by its own isn't yet enough for the more interesting
cases, namely aliases of explicit template instantiations, such as

using Ptr = std::shared_ptr<int>;

Here, we still don't show any size information, since we don't track
that information properly. In the builder, we only encounter std::shared_ptr
as a template, which doesn't have any size information yet. We would
need to build a declaration for the template instantiation of
std::shared_ptr, at which point we could ask libclang for the concrete size...

Still, this patch goes into the right direction already, I believe.