Make SkM44 public.

Make SkM44 public to be used in embedders as SkMatrix44 is deprecated.

Bug: skia: None
Change-Id: I16ac43ec80026f1486bf151aabbd9940698be7ac
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/283836
Reviewed-by: Mike Reed <reed@google.com>
Auto-Submit: Prashant Nevase <prashant.n@samsung.com>
Commit-Queue: Mike Reed <reed@google.com>

include/core/SkM44.h

@@ -119,7 +119,7 @@ struct SkV4 {
  *      +Y goes down
  *      +Z goes into the screen (away from the viewer)
  */
-class SkM44 {
+class SK_API SkM44 {
 public:
     SkM44(const SkM44& src) = default;
     SkM44& operator=(const SkM44& src) = default;