Move Dashing filterPath to a dashing utils file

From inside GrContext, we have a need to create an SkPath an original path and
some dashing info. We do not have access to the original path effect so we need
a way to make the FilterPath function accessible outside of the effect. So I moved
the core filterPath code (and all need helper functions) out of SkDashPathEffect
and created a SkDashPath in utils to store these helper functions.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/576dcdc793a762ec63fbecdbfd5768066b548fe5

Author: egdaniel@google.com

Review URL: https://codereview.chromium.org/314623004
diff --git a/gyp/utils.gypi b/gyp/utils.gypi
index 3097446..761fbf7 100644
--- a/gyp/utils.gypi
+++ b/gyp/utils.gypi
@@ -56,6 +56,8 @@
         '<(skia_src_path)/utils/SkCanvasStateUtils.cpp',
         '<(skia_src_path)/utils/SkCubicInterval.cpp',
         '<(skia_src_path)/utils/SkCullPoints.cpp',
+        '<(skia_src_path)/utils/SkDashPath.cpp',
+        '<(skia_src_path)/utils/SkDashPathPriv.h',
         '<(skia_src_path)/utils/SkDeferredCanvas.cpp',
         '<(skia_src_path)/utils/SkDumpCanvas.cpp',
         '<(skia_src_path)/utils/SkEventTracer.cpp',