`<variant>`: Add `type()` and `value()` intrinsics to `STL.natvis`?

In trying to make nice debugger natvis for an abstract syntax tree, I have found myself wishing that std::variant supported a .value() and .type() debugger intrinsic (like std::any and many other STL types do). It clearly has this information - it's able to visualize an index and [value] field. But there doesn't seem to be any way to get the type name (i.e. extract just the current index's type name from the template parameters that * matched) or display only the value (without "index=... ") in my own type's <DisplayString>.

So it would be nice if the STL.natvis could offer these too.

Start in STL.natvis and compare the existing std::any intrinsic definitions with the std::variant visualization, especially its index and [value] fields. Determine how the natvis can expose the active alternative's type and value, then verify that custom AST DisplayString entries can use both without showing the index.