Merge misc changes from docking branch to reduce small drift.

In particular:
- imgui.cpp : move UpdateInputEvents() higher in NewFrame() to match docking + update RenderMouseCursor() to match.
- imgui_draw.cpp: ImDrawList::_ResetForNewFrame() change from c807192ab
- Backends: SDL2. Add MouseWindowID + change SDL_CaptureMouse() test to match docking branch. Not strictly necessary but aimed at reducing drift because we go on and fork this file.
+ moved responsability of checking valid names to TabBarGetTabName() to simplify both branches.

backends/imgui_impl_wgpu.cpp

@@ -4,7 +4,7 @@
 
 // Implemented features:
 //  [X] Renderer: User texture binding. Use 'WGPUTextureView' as ImTextureID. Read the FAQ about ImTextureID!
-//  [X] Renderer: Support for large meshes (64k+ vertices) with 16-bit indices.
+//  [X] Renderer: Large meshes support (64k+ vertices) with 16-bit indices.
 
 // You can use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.
 // Prefer including the entire imgui/ repository into your project (either as a copy or as a submodule), and only build the backends you need.
@@ -685,7 +685,7 @@ void ImGui_ImplWGPU_InvalidateDeviceObjects()
     SafeRelease(g_resources);
 
     ImGuiIO& io = ImGui::GetIO();
-    io.Fonts->SetTexID(nullptr); // We copied g_pFontTextureView to io.Fonts->TexID so let's clear that as well.
+    io.Fonts->SetTexID(0); // We copied g_pFontTextureView to io.Fonts->TexID so let's clear that as well.
 
     for (unsigned int i = 0; i < g_numFramesInFlight; i++)
         SafeRelease(g_pFrameResources[i]);