Make SkM44 public

Need to migrate clients from private/ to core/ include
Unexperimentalize concat44() methods on SkCanvas

Change-Id: I64b8816722a9d93316cb8b8691d2d9a3e36f167f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/272464
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/src/sksl/SkSLHCodeGenerator.cpp b/src/sksl/SkSLHCodeGenerator.cpp
index 3898c05..65db84a 100644
--- a/src/sksl/SkSLHCodeGenerator.cpp
+++ b/src/sksl/SkSLHCodeGenerator.cpp
@@ -349,7 +349,7 @@
                  fFullName.c_str(),
                  fFullName.c_str());
     this->writef("#include \"include/core/SkTypes.h\"\n");
-    this->writef("#include \"include/private/SkM44.h\"\n");
+    this->writef("#include \"include/core/SkM44.h\"\n");
     this->writeSection(HEADER_SECTION);
     this->writef("\n"
                  "#include \"src/gpu/GrCoordTransform.h\"\n"