harktech: move vendored mdns into deps_src/ per repo convention

Per @SoftFever review on #13752, third-party vendored libraries belong in
deps_src/ alongside expat, imgui, hidapi, etc.

- All 5 files (mdns.{h,c}, cxmdns.{h,cpp}, NOTICE.md) move from
  src/slic3r/Utils/mdns/ to deps_src/mdns/.
- deps_src/mdns/CMakeLists.txt builds mdns as a STATIC library and scopes
  the MSVC Iphlpapi/Ws2_32 link requirement to that target instead of
  libslic3r_gui's global MSVC block.
- deps_src/CMakeLists.txt gains add_subdirectory(mdns).
- src/slic3r/CMakeLists.txt drops the inline source listings and links
  libslic3r_gui against the new mdns target; MSVC block keeps only
  Setupapi.lib.
- src/slic3r/Utils/CrealityHostDiscovery.cpp #include updated to use the
  include dir exposed by the new mdns target.

Verified by a clean Linux build (orca-slicer links successfully).

deps_src/CMakeLists.txt

@@ -27,6 +27,7 @@ add_subdirectory(libigl)
 add_subdirectory(libnest2d)
 add_subdirectory(mcut)
 add_subdirectory(md4c)
+add_subdirectory(mdns)
 add_subdirectory(miniz)
 add_subdirectory(minilzo)
 add_subdirectory(qhull)

deps_src/mdns/CMakeLists.txt

@@ -0,0 +1,19 @@
+cmake_minimum_required(VERSION 3.13)
+
+project(mdns)
+
+# Static library wrapping mjansson/mdns (public domain) plus the cxmdns C++
+# wrapper from CrealityPrint v7.1.1 (AGPL-3.0). See NOTICE.md for attribution.
+add_library(mdns STATIC
+    mdns.h
+    mdns.c
+    cxmdns.h
+    cxmdns.cpp
+)
+
+target_include_directories(mdns SYSTEM PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
+
+if (MSVC)
+    # mjansson/mdns uses GetAdaptersAddresses (Iphlpapi) and Winsock2 (Ws2_32).
+    target_link_libraries(mdns PUBLIC Iphlpapi Ws2_32)
+endif()

src/slic3r/CMakeLists.txt

@@ -669,10 +669,6 @@ set(SLIC3R_GUI_SOURCES
     Utils/WxFontUtils.hpp
     Utils/FileTransferUtils.cpp
     Utils/FileTransferUtils.hpp
-    Utils/mdns/mdns.h
-    Utils/mdns/mdns.c
-    Utils/mdns/cxmdns.h
-    Utils/mdns/cxmdns.cpp
 )
 
 add_subdirectory(GUI/DeviceCore)
@@ -762,13 +758,11 @@ else()
     set(_opengl_link_lib OpenGL::GL)
 endif()
 
-target_link_libraries(libslic3r_gui libslic3r cereal::cereal imgui imguizmo minilzo libvgcode md4c-html glad ${_opengl_link_lib} hidapi ${wxWidgets_LIBRARIES} glfw libcurl OpenSSL::SSL OpenSSL::Crypto noise::noise)
+target_link_libraries(libslic3r_gui libslic3r cereal::cereal imgui imguizmo minilzo libvgcode md4c-html glad ${_opengl_link_lib} hidapi mdns ${wxWidgets_LIBRARIES} glfw libcurl OpenSSL::SSL OpenSSL::Crypto noise::noise)
 
 
 if (MSVC)
-    # Iphlpapi/Ws2_32 are required by the vendored mjansson/mdns library
-    # (GetAdaptersAddresses + Winsock2) used by CrealityHostDiscovery.
-    target_link_libraries(libslic3r_gui Setupapi.lib Iphlpapi.lib Ws2_32.lib)
+    target_link_libraries(libslic3r_gui Setupapi.lib)
 elseif (CMAKE_SYSTEM_NAME STREQUAL "Linux")
     FIND_LIBRARY(WAYLAND_SERVER_LIBRARIES NAMES wayland-server)
     FIND_LIBRARY(WAYLAND_EGL_LIBRARIES    NAMES wayland-egl)

src/slic3r/Utils/CrealityHostDiscovery.cpp

@@ -1,5 +1,5 @@
 #include "CrealityHostDiscovery.hpp"
-#include "mdns/cxmdns.h"
+#include "cxmdns.h"
 #include "Http.hpp"
 
 #include <boost/log/trivial.hpp>