Show definition of underlying struct when hovering over a typedef

[HighCommander4]

In #959, I posted a patch to show the public fields of the struct when hovering over a struct name.

In some codebases, structs are typically referred to via a typedef (especially in C, where a typedef allows omitting the struct keyword), so it would be helpful to extend this to also show the struct members when hovering over a typedef that resolves to a struct name.

[HighCommander4]

This can actually be decoupled from #959. I adjusted the title of this issue to track a more general change where, when hovering over a typedef to a struct, the definition of the underlying struct is shown in addition to the definition of the typedef.

This is orthogonal to whether the definition of the struct that's shown includes its members (#959).