The data constructed by this call remains in the 'C-alloc' realm, i.e.
it can be `MEM_dupallocN`'ed, and `MEM_freeN`'ed.
This is intended as a temporary API only, to facilitate transition to
full C++ handling of data in Blender. It's primary target is to allow
pseudo-POD types to use default values for their members. See e.g.
!134531.
Unlike !143827 and !138829, it does not change the current rule (`new`
must be paired with `delete`, and `alloc` must be paired with `free`).
Instead, it defines an explicit and temporary API to allow a very
limited form of construction to happen on C-allocated data, provided
that the type is default-constructible, and remains trivial after
construction.
### Notes
* The new API is purposely as restrictive as possible, trying to
only allow the current known needs (init with default member values).
This can easily be extended if needed.
* To try to stay as close as malloc/calloc behavior as possible, and
avoid the 'zero-initialization' gotcha, it does not use
value-initialization, but instead default-initialization on zero-
initialized memory.
_Ideally it would even not allow any user-defined default constructor,
but this does not seem simple to detect._
Pull Request: https://projects.blender.org/blender/blender/pulls/144141
307d0de26e