Fix rendering errors caused by dragging the window across monitors with different DPI scaling.

[the-loki]

When I create a window using the docking branch and enable the following settings, some rendering issues occur when dragging between monitors with different DPI scaling.

io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard;
io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad;
io.ConfigFlags |= ImGuiConfigFlags_DockingEnable;
io.ConfigFlags |= ImGuiConfigFlags_ViewportsEnable;

io.ConfigViewportsNoAutoMerge = true;
io.ConfigViewportsNoTaskBarIcon = false;
io.ConfigViewportsNoDefaultParent = true;
io.ConfigViewportsNoDecoration = true;

I found that dragging in NoDecoration mode relies on using glfwSetWindowPos, and the window triggers a resize when crossing monitors. However, the resize triggered by glfwSetWindowPos occurs immediately in the current frame, which means some operations depending on PlatformRequestResize might have already completed. Additionally, the PlatformRequestResize flag is cleared at the end of the frame. Therefore, we need to consider delaying the resize triggered by glfwSetWindowPos to the next frame to ensure that operations related to PlatformRequestResize are fully executed.

I only handled the related issue in GLFW, but other backends might have similar problems. Perhaps other window events could also have similar issues (triggered in the current frame but not fully processed before being cleared).

The related issues:

#7689 #6444

[the-loki]

@ocornut
Is there anything else I need to do to move forward with this PR?