Cleanup/refactor: Rename BKE_library files to BKE_lib.

Note that `BKE_library.h`/`library.c` were renamed to
`BKE_lib_id.h`/`lib_id.c` to avoid having a too generic name here.

Part of T72604.

source/blender/blenkernel/intern/mask.c

@@ -46,7 +46,7 @@
 #include "BKE_animsys.h"
 #include "BKE_curve.h"
 
-#include "BKE_library.h"
+#include "BKE_lib_id.h"
 #include "BKE_main.h"
 #include "BKE_mask.h"
 #include "BKE_node.h"
@@ -883,7 +883,7 @@ Mask *BKE_mask_copy_nolib(Mask *mask)
  *
  * WARNING! This function will not handle ID user count!
  *
- * \param flag: Copying options (see BKE_library.h's LIB_ID_COPY_... flags for more).
+ * \param flag: Copying options (see BKE_lib_id.h's LIB_ID_COPY_... flags for more).
  */
 void BKE_mask_copy_data(Main *UNUSED(bmain),
                         Mask *mask_dst,