The (out caller-allocates) and (out callee-allocates) annotations are meant for structured or pointer types. Plain old data types are just regular out parameters and don't need the annotation about who allocates them. See glib!2005, gjs#570
This is a helper to compute the bounds for stroke nodes. We keep it private for now.
A GskStroke struct collects the parameters that are needed for stroking a path.
