Add `name` to base class descriptors

[pdimov]

The macros receive it, and the reflection TS also provides it.

[reddwarf69]

What about the name of the main class?

I could make use of it in something like https://www.boost.org/doc/libs/1_82_0/libs/describe/doc/html/describe.html#example_fmtlib_class_formatter. typeid(t).name() is not the same.

(or should this be handled via https://www.boost.org/doc/libs/release/doc/html/boost_typeindex.html ?)

[pdimov]

Makes sense in principle but I'd need to add another primitive, describe_type<T>, from which to return it, as there's no good place for it in the existing ones.