rewrite includes to not need so much -Ifoo

Current strategy: everything from the top

Things to look at first are the manual changes:

   - added tools/rewrite_includes.py
   - removed -Idirectives from BUILD.gn
   - various compile.sh simplifications
   - tweak tools/embed_resources.py
   - update gn/find_headers.py to write paths from the top
   - update gn/gn_to_bp.py SkUserConfig.h layout
     so that #include "include/config/SkUserConfig.h" always
     gets the header we want.

No-Presubmit: true
Change-Id: I73a4b181654e0e38d229bc456c0d0854bae3363e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/209706
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Hal Canary <halcanary@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
diff --git a/samplecode/SampleCusp.cpp b/samplecode/SampleCusp.cpp
index d978e33..b287bbd 100644
--- a/samplecode/SampleCusp.cpp
+++ b/samplecode/SampleCusp.cpp
@@ -6,12 +6,12 @@
  */
 
 #include <string>
-#include "AnimTimer.h"
-#include "Sample.h"
-#include "SkCanvas.h"
-#include "SkFont.h"
-#include "SkGeometry.h"
-#include "SkPath.h"
+#include "include/core/SkCanvas.h"
+#include "include/core/SkFont.h"
+#include "include/core/SkPath.h"
+#include "samplecode/Sample.h"
+#include "src/core/SkGeometry.h"
+#include "tools/timer/AnimTimer.h"
 
 // This draws an animation where every cubic has a cusp, to test drawing a circle
 // at the cusp point. Create a unit square. A cubic with its control points