BUG: Address issues related to ITK update to modern interfaces

Recent changes to ITK have been made to use CMake interfaces over raw
libraries and files, along with adding the ITK namespace to targets:
See InsightSoftwareConsortium/ITK#5721

This change consistently uses the proxTV namespace for compatibility
between uses of the proxTV.

Author: blowekamp

CMakeLists.txt

@@ -1,13 +1,9 @@
 cmake_minimum_required(VERSION 3.16.2)
 project(TotalVariation)
 
-if(ITK_USE_SYSTEM_proxTV)
-  set(TotalVariation_LIBRARIES proxTV::proxTV)
-else()
-  set(TotalVariation_LIBRARIES proxTV)
-endif()
 
-set(${PROJECT_NAME}_THIRD_PARTY 1)
+set(TotalVariation_LIBRARIES proxTV::proxTV)
+
 
 include(itk-module-init.cmake)
 
@@ -53,12 +49,9 @@ else()
   add_compile_definitions(PROXTV_USE_LAPACK)
 endif()
 
-# _proxTV_lib will be `proxTV::proxTV` when find_package, and `proxTV` when add_subdirectory(proxTV_folder)
-set(_proxTV_lib "")
 # if proxTV is built elsewhere
 if(ITK_USE_SYSTEM_proxTV)
   find_package(proxTV REQUIRED CONFIG)
-  set(_proxTV_lib proxTV::proxTV)
   set(proxTV_DIR_INSTALL ${proxTV_DIR})
   set(proxTV_DIR_BUILD ${proxTV_DIR})
   # It is only needed to EXPORT_CODE_BUILD when using external proxTV
@@ -110,12 +103,12 @@ else() # build proxTV here with the selected Eigen3
     endif()
     set(proxTV_INSTALL_CMAKE_DIR ${ITK_INSTALL_PACKAGE_DIR}/Modules)
   endif()
+  #set(proxTV_INSTALL_DEVELOPMENT OFF)
   # end proxTV options
 
   FetchContent_MakeAvailable(proxTV_fetch)
   # proxTV will generate a target proxTV::proxTV when using find_package,
-  # or a library proxTV when using add_subdirectory
-  set(_proxTV_lib proxTV) # proxTV generated in subdirectory
+
   set(proxTV_DIR_INSTALL "${CMAKE_INSTALL_PREFIX}/${proxTV_INSTALL_CMAKE_DIR}")
 endif()
 
@@ -130,7 +123,7 @@ find_package(proxTV REQUIRED CONFIG)
 set(_populate_include_dirs_for_swig TRUE)
 if(${_populate_include_dirs_for_swig})
   # SWIG (wrapping) requires INCLUDE_DIRS
-  get_target_property(proxTV_INCLUDE_DIRS ${_proxTV_lib} INTERFACE_INCLUDE_DIRECTORIES)
+  get_target_property(proxTV_INCLUDE_DIRS proxTV::proxTV INTERFACE_INCLUDE_DIRECTORIES)
   string(REGEX REPLACE
     ".*BUILD_INTERFACE:(.*/proxtv_fetch-build/src/include).*"
     "\\1"
@@ -151,5 +144,3 @@ else()
 endif()
 
 
-# Add the proxTV library to Modules/Targets/TotalVariationTargets.cmake
-itk_module_target(${_proxTV_lib} NO_INSTALL)