Move Sk3Perspective and Sk3Lookat into SkM44

Sk3Perspective -> SkM44::Perspective
Sk3LookAt -> SkM44::LookAt

Also adds some SK_API tags to the SkV[2,3,4] structs. Also fixes
linkage issues around Sk3Perspective/LookAt by moving them into the
exported SkM44 (if we don't like them as SkM44 factories, will just need
to add SK_API tags to old Sk3Perspective/Lookat directly).

Change-Id: I3f125211b76899f216e63cc8d587776004516e36
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/388476
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
diff --git a/samplecode/Sample3D.cpp b/samplecode/Sample3D.cpp
index 5bfb00c..575110a 100644
--- a/samplecode/Sample3D.cpp
+++ b/samplecode/Sample3D.cpp
@@ -86,8 +86,8 @@
 
 public:
     void concatCamera(SkCanvas* canvas, const SkRect& area, SkScalar zscale) {
-        SkM44 camera = Sk3LookAt(fEye, fCOA, fUp),
-              perspective = Sk3Perspective(fNear, fFar, fAngle),
+        SkM44 camera = SkM44::LookAt(fEye, fCOA, fUp),
+              perspective = SkM44::Perspective(fNear, fFar, fAngle),
               viewport = SkM44::Translate(area.centerX(), area.centerY(), 0) *
                          SkM44::Scale(area.width()*0.5f, area.height()*0.5f, zscale);