I want to understand how calls to `new` for classes and structs
are lowered by the compiler and druntime to a GC-allocation
(specifically how the `ba`-argument bits are determined) followed
by an initialization using default constructor or via a
user-defined constructor called using arguments to `new`. And how
this is related to the trait `hasElaborateConstructor` for both
`classes` and `structs`.
I also want to understand how manually defined constructors and
destructors affect the setting of the GC finalizer for a given
aggregate type. And how this is related to the trait
`hasElaborateDestructor` for both `classes` and `structs`.
Where's the dmd and druntime code that handles these steps?
