Retract GrSurfaceDrawContext.h a bit

This CL just pulls GrSurfaceDrawContext.h out of headers and .cpp files where possible.

TBR=brianosman@google.com
Bug: skia:11837
Change-Id: Ib96f3619e3a50091516f81ae48f956fe83c05aff
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/431384
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
diff --git a/gn/gm.gni b/gn/gm.gni
index 3c36037..302a69b 100644
--- a/gn/gm.gni
+++ b/gn/gm.gni
@@ -72,6 +72,7 @@
   "$_gm/circle_sizes.cpp",
   "$_gm/circulararcs.cpp",
   "$_gm/circularclips.cpp",
+  "$_gm/clear_swizzle.cpp",
   "$_gm/clip_error.cpp",
   "$_gm/clip_sierpinski_region.cpp",
   "$_gm/clip_strokerect.cpp",
@@ -403,7 +404,6 @@
   "$_gm/aarecteffect.cpp",
   "$_gm/beziereffects.cpp",
   "$_gm/bigrrectaaeffect.cpp",
-  "$_gm/clear_swizzle.cpp",
   "$_gm/clockwise.cpp",
   "$_gm/constcolorprocessor.cpp",
   "$_gm/convexpolyeffect.cpp",