Move SkSpan to include/, for use in public API

Change-Id: I674f038600afd6d49316c1ece515941ee5579068
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/406939
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/fuzz/FuzzSkParagraph.cpp b/fuzz/FuzzSkParagraph.cpp
index 0c66225..f4765f9 100644
--- a/fuzz/FuzzSkParagraph.cpp
+++ b/fuzz/FuzzSkParagraph.cpp
@@ -19,6 +19,7 @@
 #include "include/core/SkRect.h"
 #include "include/core/SkRefCnt.h"
 #include "include/core/SkScalar.h"
+#include "include/core/SkSpan.h"
 #include "include/core/SkStream.h"
 #include "include/core/SkString.h"
 #include "include/core/SkTypeface.h"
@@ -37,7 +38,6 @@
 #include "modules/skparagraph/src/TextLine.h"
 #include "modules/skparagraph/utils/TestFontCollection.h"
 #include "src/core/SkOSFile.h"
-#include "src/core/SkSpan.h"
 #include "src/utils/SkOSPath.h"
 #include "src/utils/SkShaperJSONWriter.h"
 #include "tests/Test.h"