Fix union logic between metaclasses of uninstantiated generic classes in same hierarchy

[HertzDevil]

#10527 introduced a reducible union that didn't previously exist:

class Foo(T)
end

class Bar(T) < Foo(T)
end

typeof(Foo || Bar) # => (Bar(T).class | Foo(T).class)
# before:          # => Foo(T).class

It happened because Foo and Bar were handled like normal classes instead of metaclasses (every Crystal::MetaclassType is a ClassType), and because Type#depth isn't really used for metaclasses yet; changing the overload order of the least common ancestor method fixes this.

[asterite]

Can we move the Type vs Type overload to the bottom? It feels weird to me that it's the first overload, I always put the least general one at the bottom, just in case.