Backends: DirectX12: Texture upload use the command queue provided in ImGui_ImplDX12_InitInfo instead of creating its own.

+ minor tweaks to faciliate branch merging.

imgui.cpp

@@ -5086,6 +5086,7 @@ void ImGui::UpdateHoveredWindowAndCaptureFlags()
 }
 
 // Called once a frame. Followed by SetCurrentFont() which sets up the remaining data.
+// FIXME-VIEWPORT: the concept of a single ClipRectFullscreen is not ideal!
 static void SetupDrawListSharedData()
 {
     ImGuiContext& g = *GImGui;