render/gles2: add wlr_renderer_is_gles2

Export the interface used to determine whether the wlr_renderer object
is gles2.

include/wlr/render/gles2.h

@@ -30,6 +30,7 @@ struct wlr_gles2_texture_attribs {
 	bool has_alpha;
 };
 
+bool wlr_renderer_is_gles2(struct wlr_renderer *wlr_renderer);
 bool wlr_texture_is_gles2(struct wlr_texture *texture);
 void wlr_gles2_texture_get_attribs(struct wlr_texture *texture,
 	struct wlr_gles2_texture_attribs *attribs);

render/gles2/renderer.c

@@ -28,9 +28,13 @@ static const GLfloat verts[] = {
 
 static const struct wlr_renderer_impl renderer_impl;
 
+bool wlr_renderer_is_gles2(struct wlr_renderer *wlr_renderer) {
+	return wlr_renderer->impl == &renderer_impl;
+}
+
 struct wlr_gles2_renderer *gles2_get_renderer(
 		struct wlr_renderer *wlr_renderer) {
-	assert(wlr_renderer->impl == &renderer_impl);
+	assert(wlr_renderer_is_gles2(wlr_renderer));
 	return (struct wlr_gles2_renderer *)wlr_renderer;
 }