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
Allows to speed up lookups like "is property FOO of data BAR animated".
Can be used to optimize object's visibility check, but also allows to
check animation on bones without too much of time penalty.
The cache is shared between both nodes and relations builder.
Currently is not used, just a boilerplate for an upcoming changes in
an actual logic.
