[Reland] Relocate shaders to own dir

Consolidate all shader impls under src/shaders/.

(reland of https://skia-review.googlesource.com/c/17927/)

Change-Id: I7918bdc1aafe842ed194412ba95b9ae53a2ec1d7
Reviewed-on: https://skia-review.googlesource.com/18146
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
diff --git a/public.bzl b/public.bzl
index ba3b3b0..722c126 100644
--- a/public.bzl
+++ b/public.bzl
@@ -442,6 +442,7 @@
     "src/ports",
     "src/pdf",
     "src/sfnt",
+    "src/shaders",
     "src/sksl",
     "src/utils",
     "third_party/etc1",
@@ -544,12 +545,13 @@
     "src/codec",
     "src/core",
     "src/effects",
-    "src/effects/gradients",
     "src/fonts",
     "src/images",
     "src/pathops",
     "src/pipe/utils",
     "src/ports",
+    "src/shaders",
+    "src/shaders/gradients",
     "src/xml",
     "tests",
     "tools",