Move SkGLContext and some GrGLInterface implementations to skgputest module

src/gpu/gl/mesa/GrGLCreateMesaInterface.cpp

-/*
- * Copyright 2011 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#include "gl/GrGLAssembleInterface.h"
-#include "../GrGLUtil.h"
-
-#include "osmesa_wrapper.h"
-
-static GrGLFuncPtr osmesa_get(void* ctx, const char name[]) {
-    SkASSERT(nullptr == ctx);
-    SkASSERT(OSMesaGetCurrentContext());
-    return OSMesaGetProcAddress(name);
-}
-
-const GrGLInterface* GrGLCreateMesaInterface() {
-    if (nullptr == OSMesaGetCurrentContext()) {
-        return nullptr;
-    }
-    return GrGLAssembleInterface(nullptr, osmesa_get);
-}