[core] Move GLFW stencil clip debug to core

This makes the stencil clip debug available to all platforms.

Fixes #4669.

include/mbgl/map/mode.hpp

@@ -43,6 +43,10 @@ enum class MapDebugOptions : EnumType {
     Timestamps  = 1 << 3,
     Collision   = 1 << 4,
     Wireframe   = 1 << 5,
+// FIXME: https://github.com/mapbox/mapbox-gl-native/issues/5117
+#ifndef GL_ES_VERSION_2_0
+    StencilClip = 1 << 6,
+#endif // GL_ES_VERSION_2_0
 };
 
 inline MapDebugOptions operator| (const MapDebugOptions& lhs, const MapDebugOptions& rhs) {

include/mbgl/platform/default/glfw_view.hpp

@@ -49,9 +49,6 @@ private:
     makeSpriteImage(int width, int height, float pixelRatio);
 
     void nextOrientation();
-    void toggleClipMasks();
-
-    void renderClipMasks();
 
     void addRandomPointAnnotations(int count);
     void addRandomShapeAnnotations(int count);
@@ -81,8 +78,6 @@ private:
     int fbHeight;
     float pixelRatio;
 
-    bool showClipMasks = false;
-
     double lastX = 0, lastY = 0;
 
     double lastClick = -1;