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/gm/bitmappremul.cpp b/gm/bitmappremul.cpp
index a899510..489fed9 100644
--- a/gm/bitmappremul.cpp
+++ b/gm/bitmappremul.cpp
@@ -5,10 +5,10 @@
  * found in the LICENSE file.
  */
 
-#include "gm.h"
-#include "SkBitmap.h"
-#include "SkCanvas.h"
-#include "SkColorData.h"
+#include "gm/gm.h"
+#include "include/core/SkBitmap.h"
+#include "include/core/SkCanvas.h"
+#include "include/private/SkColorData.h"
 
 /**
  * This GM checks that bitmap pixels are unpremultiplied before being exported