ENH: Bump elastix version to 2023-05-15, use C++17

Including:

  pull request SuperElastix/elastix#891
  commit SuperElastix/elastix@ed15547
  "PERF: Fill `jsj` (JacobianOfSpatialJacobian) in-place and remove `jsj1`"

  pull request SuperElastix/elastix#890
  commit SuperElastix/elastix@b9ea3a8
  "PERF: Fill `jsh` (JacobianOfSpatialJacobian) in-place and remove `jsh1`"

  pull request SuperElastix/elastix#887
  commit SuperElastix/elastix@8298485
  PERF: Make EvaluateParzenValues calls faster, using raw buffer of values

  pull request SuperElastix/elastix#882
  commit SuperElastix/elastix@58e0a7b
  "ENH: Convert the input images to the user-specified internal pixel type"

  pull request SuperElastix/elastix#864
  commit SuperElastix/elastix@c3d478e
  "ENH: Upgrade elastix from C++14 to C++17"

  pull request SuperElastix/elastix#856
  commit SuperElastix/elastix@48c6458
  "ENH: Add SetInitialTransformParameterObject to ElastixRegistrationMethod"

  pull request SuperElastix/elastix#832
  commit SuperElastix/elastix@05d2b40
  ENH: Support "ShowProgressPercentage" parameter (`false` by default)

  pull request SuperElastix/elastix#815
  commit SuperElastix/elastix@c4ef707
  "ENH: Add `ElastixLogLevel` to the ITK interface"

Explicitly specified C++17 as standard for the compilation of ITKElastix.

CMakeLists.txt

@@ -1,6 +1,11 @@
 cmake_minimum_required(VERSION 3.16.3)
 project(Elastix)
 
+if(NOT CMAKE_CXX_STANDARD)
+  # SuperElastix/elastix uses C++17 specific features in some of its header files.
+  set(CMAKE_CXX_STANDARD 17)
+endif()
+
 # To ease enablement with Python packaging
 if(DEFINED ENV{ELASTIX_USE_OPENCL})
   set(ELASTIX_USE_OPENCL ON CACHE BOOL "Enable OpenCL support in Elastix")
@@ -51,7 +56,7 @@ if(SKBUILD)
 endif()
 
 set(elastix_GIT_REPOSITORY "https://github.com/SuperElastix/elastix.git")
-set(elastix_GIT_TAG "d652938573e5f193955908eba225a854b31ce36a")
+set(elastix_GIT_TAG "b9b8e20aef83f94ed38a81cc38625a1bfddf1053")
 FetchContent_Declare(
   elx
   GIT_REPOSITORY ${elastix_GIT_REPOSITORY}