Add GrGLMakeNativeInterface factory that returns sk_sp<const GrGLInterface>.

Removes the concept of a configurable "default" interface and makes the default
always be the "native" interface.

Also removes unused functions: GrGLInterfaceAddTestDebugMarker and
GrGLInterface::NewClone.

Keeps around legacy GrGLCreateNativeInterface() until clients can be weened.

Change-Id: I4a3bdafa8cf8c68ed13318393abd55686b045ccb
Reviewed-on: https://skia-review.googlesource.com/83000
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/example/SkiaSDLExample.cpp b/example/SkiaSDLExample.cpp
index ab181cb..3e23e57 100644
--- a/example/SkiaSDLExample.cpp
+++ b/example/SkiaSDLExample.cpp
@@ -189,7 +189,7 @@
     glClear(GL_COLOR_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
 
     // setup GrContext
-    sk_sp<const GrGLInterface> interface(GrGLCreateNativeInterface());
+    auto interface = GrGLMakeNativeInterface();
 
     // setup contexts
     sk_sp<GrContext> grContext(GrContext::MakeGL(interface));