Move SkGLContext and some GrGLInterface implementations to skgputest module

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1815823002
CQ_EXTRA_TRYBOTS=client.skia.compile:Build-Ubuntu-GCC-x86_64-Release-CMake-Trybot,Build-Mac-Clang-x86_64-Release-CMake-Trybot

Committed: https://skia.googlesource.com/skia/+/fe3456cb006110d045b26ff3f8681b893a757b58

Review URL: https://codereview.chromium.org/1815823002
diff --git a/dm/DMSrcSink.cpp b/dm/DMSrcSink.cpp
index 9e9ba9e..e704f74 100644
--- a/dm/DMSrcSink.cpp
+++ b/dm/DMSrcSink.cpp
@@ -45,6 +45,8 @@
             " into multiple pages");
 DEFINE_bool(RAW_threading, true, "Allow RAW decodes to run on multiple threads?");
 
+using sk_gpu_test::GrContextFactory;
+
 namespace DM {
 
 GMSrc::GMSrc(skiagm::GMRegistry::Factory factory) : fFactory(factory) {}