Cleanup: CMake: Modernize bf_intern_utfconv dependencies

- Remove any bf_intern_utfconv paths from INC
- Add a dependency though LIB when missing
- an empty target is created for non windows builds, so we don't have to
if(WIN32) this all over the place

context: https://devtalk.blender.org/t/cmake-cleanup/30260
Pull Request: https://projects.blender.org/blender/blender/pulls/115373

intern/utfconv/CMakeLists.txt

@@ -3,7 +3,7 @@
 # SPDX-License-Identifier: GPL-2.0-or-later
 
 set(INC
-  .
+  PUBLIC .
 )
 
 set(INC_SYS
@@ -19,14 +19,16 @@ set(SRC
 set(LIB
 )
 
-# This is odd but leave it for now...
-# Why have win32 check here? - this is only used for windows.
-# ... because one day we might want to use it on other platforms.
+# This library is currently windows only, for the other platforms an empty target is created this 
+# way we don't have to clutter if(WIN32) ... endif() all over the place to use this library.
 if(WIN32)
   list(APPEND SRC
     utf_winfunc.cc
     utf_winfunc.hh
   )
+  blender_add_lib(bf_intern_utfconv "${SRC}" "${INC}" "${INC_SYS}" "${LIB}")
+else()
+  add_library(bf_intern_utfconv INTERFACE)
 endif()
 
-blender_add_lib(bf_intern_utfconv "${SRC}" "${INC}" "${INC_SYS}" "${LIB}")
+add_library(bf::intern::utfconv ALIAS bf_intern_utfconv)