Remove const qualifier on ImTextureID local (#4060)

When defining ImTextureID to a type such as Texture*, the const-qualifier here stops us from using the texture ID. const Texture* is not valid to be pushed as a texture ID anymore.

imgui_draw.cpp

@@ -3770,7 +3770,7 @@ void ImGui::RenderMouseCursor(ImDrawList* draw_list, ImVec2 pos, float scale, Im
     if (font_atlas->GetMouseCursorTexData(mouse_cursor, &offset, &size, &uv[0], &uv[2]))
     {
         pos -= offset;
-        const ImTextureID tex_id = font_atlas->TexID;
+        ImTextureID tex_id = font_atlas->TexID;
         draw_list->PushTextureID(tex_id);
         draw_list->AddImage(tex_id, pos + ImVec2(1, 0) * scale, pos + (ImVec2(1, 0) + size) * scale,    uv[2], uv[3], col_shadow);
         draw_list->AddImage(tex_id, pos + ImVec2(2, 0) * scale, pos + (ImVec2(2, 0) + size) * scale,    uv[2], uv[3], col_shadow);