`wmDragActiveDropState` contains a `bContextStore` unique pointer, so
when constructing/destructing an object of this type `BKE_context.hh`
had to be included. It wouldn't be obvious why this include is necessary
in some cases. And the pointer is otherwise managed internally in the
source file, so the need for this include shouldn't bleed into other
files.
Make sure the unique pointer construction/destruction happens in the
translation unit of the source file that otherwise also manages it.
Avoids include in #107230.
e3b3399bcb