The old layout of `PointerRNA` was confusing for historic reasons: ``` typedef struct PointerRNA { struct { void *data; } id; struct StructRNA *type; void *data; } PointerRNA; ``` This patch updates it to: ``` typedef struct PointerRNA { struct ID *owner_id; struct StructRNA *type; void *data; } PointerRNA; ``` Throughout the code base `id.data` was replaced with `owner_id`. Furthermore, many explicit pointer type casts were added which were implicit before. Some type casts to `ID *` were removed. Reviewers: brecht, campbellbarton Differential Revision: https://developer.blender.org/D5558