Fix FBX SDK linking errors on Linux for static builds

The io_marker_test was failing to link on Linux CI because the FBX SDK
static library requires zlib and libdl dependencies that weren't being
linked.

Changes:
- cmake/FindFbxSdk.cmake: Added ZLIB and libdl (via CMAKE_DL_LIBS) to
  the Linux dependencies list. This fixes undefined references to zlib
  functions (deflate, inflate, crc32, adler32) and libdl functions
  (dlopen, dlclose, dlsym).

- cmake/momentum-config.cmake.in: Added conditional find_dependency for
  FbxSdk when MOMENTUM_ENABLE_FBX_SAVING is enabled. This ensures
  downstream projects can properly link against momentum when built with
  FBX SDK support as static libraries.

- CMakeLists.txt: Added FindFbxSdk.cmake to the install command so the
  finder module is available to downstream projects.

Fixes: https://github.com/facebookresearch/momentum/actions/runs/19022913829/job/54321176648?pr=753

Author: jeongseok-meta

CMakeLists.txt

@@ -920,7 +920,7 @@ install(
 
 # Install CMake modules
 install(
-  FILES cmake/Findre2.cmake
+  FILES cmake/Findre2.cmake cmake/FindFbxSdk.cmake
   DESTINATION ${MOMENTUM_CONFIG_INSTALL_DIR}
 )
 

cmake/FindFbxSdk.cmake

@@ -86,9 +86,10 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Darwin")
   list(APPEND required_vars LibXml2_FOUND Iconv_FOUND ZLIB_LIBRARIES)
 elseif(CMAKE_SYSTEM_NAME STREQUAL "Linux")
   find_package(LibXml2 MODULE QUIET)
-  list(APPEND FBXSDK_LIBRARIES LibXml2::LibXml2)
-  list(APPEND FBXSDK_LIBRARIES_DEBUG LibXml2::LibXml2)
-  list(APPEND required_vars LibXml2_FOUND)
+  find_package(ZLIB MODULE QUIET)
+  list(APPEND FBXSDK_LIBRARIES LibXml2::LibXml2 ${ZLIB_LIBRARIES} ${CMAKE_DL_LIBS})
+  list(APPEND FBXSDK_LIBRARIES_DEBUG LibXml2::LibXml2 ${ZLIB_LIBRARIES} ${CMAKE_DL_LIBS})
+  list(APPEND required_vars LibXml2_FOUND ZLIB_LIBRARIES)
 endif()
 
 # Set (NAME)_FOUND if all the variables and the version are satisfied.

cmake/momentum-config.cmake.in

@@ -36,6 +36,10 @@ if(@MOMENTUM_ENABLE_PROFILING@)
   find_dependency(Tracy CONFIG)
 endif()
 
+if(@MOMENTUM_ENABLE_FBX_SAVING@)
+  find_dependency(FbxSdk MODULE)
+endif()
+
 list(REMOVE_AT CMAKE_MODULE_PATH -1)
 
 include("${CMAKE_CURRENT_LIST_DIR}/@[email protected]")