Route canvas layer GL state through backend

src/renderer_gl/opengl_capabilities.cpp

@@ -844,8 +844,9 @@ pp::foundation::Status copy_opengl_framebuffer_to_texture_2d(
         return pp::foundation::Status::success();
     }
 
+    const auto texture_target = copy.texture_target == 0U ? texture_2d_target() : copy.texture_target;
     dispatch.copy_tex_sub_image_2d(
-        texture_2d_target(),
+        texture_target,
         copy.level,
         copy.destination_x,
         copy.destination_y,

src/renderer_gl/opengl_capabilities.h

@@ -150,6 +150,7 @@ struct OpenGlTexture2DUpdate {
 };
 
 struct OpenGlTexture2DFramebufferCopy {
+    std::uint32_t texture_target = 0;
     std::int32_t level = 0;
     std::int32_t destination_x = 0;
     std::int32_t destination_y = 0;