add typedef struct sk_bitmapallocator_t sk_bitmapallocator_t;

Author: mgood7123

include/c/sk_types.h

@@ -343,6 +343,7 @@ typedef struct sk_string_t sk_string_t;
     A sk_bitmap_t is an abstraction that specifies a raster bitmap.
 */
 typedef struct sk_bitmap_t sk_bitmap_t;
+typedef struct sk_bitmapallocator_t sk_bitmapallocator_t;
 typedef struct sk_pixmap_t sk_pixmap_t;
 typedef struct sk_colorfilter_t sk_colorfilter_t;
 // placed here to help seperate in PR