WIP: Require ITK 6 and request modules as find_package COMPONENTS

[hjmjohnson]

Require ITK 6 and request each example's modules as find_package COMPONENTS,
linking ${ITK_INTERFACE_LIBRARIES}. Supersedes #470.

Stacked on #479 — review the 12 commits from COMP: Require ITK 6 onward.

Why require ITK 6

Every example already links ITK::<Name>Module interface targets, which ITK 5.x does not export. Against ITK 5.4 the build fails with one missing-target error per example (346 in all); requiring ITK 6 stops at the first find_package with a single version error instead.

Examples for ITK 5.x live on the release-5.4 branch, created at b0679d89, the last commit that still builds with ITK 5.x (verified against ITK 5.4.7: 0 failed targets, 346 executables, 370/370 tests).

What the conversion does, and the two rules it follows

Each example's ITK::<Name>Module link targets become find_package components, and the link list becomes ${ITK_INTERFACE_LIBRARIES}:

-find_package(ITK REQUIRED)
+find_package(
+  ITK
+  REQUIRED
+  COMPONENTS
+    ITKImageIO
+    ITKThresholding
+)
 itk_generate_factory_registration()
 target_link_libraries(
   ${PROJECT_NAME}
   PRIVATE
+    ${ITK_INTERFACE_LIBRARIES}
     ITK::ITKImageIO
-    ITK::ITKThresholdingModule
 )

Two rules the script applies, both load-bearing:

1. Component names are module names, not target names — ITKAnisotropicSmoothing, not ITK::ITKAnisotropicSmoothingModule. Naming a target here stops the configure with No such module.
2. Factory meta-modules stay explicitly linked (ITKImageIO, ITKMeshIO, ITKTransformIO, ITKFFTImageFilterInit), because linking the meta-module is what enables the generated registration code. ITKVtkGlue and ITKVideoBridgeOpenCV stay explicit links and are deliberately not components: they are conditional, so requiring them would break every VTK-less or OpenCV-less build.

Commits are one per top-level src/ directory, from 12 files in Bridge to 183 in Filtering.

Verification

Built against ITK main with Module_ITKVtkGlue=ON and Python wrapping enabled, then run through the project's own ctest suite:

	before	after
build	0 failed targets, 365 executables	0 failed targets, 365 executables
tests	200 failures of 558	identical set

0 new failures, 0 newly passing. The conversion is behavior-neutral, which is the intent: it changes how modules are requested, not what gets linked. Spot-checked on one example that the executable links the same 52 ITK libraries, registers the same 24 ImageIO factories, and produces byte-identical output.

pre-commit run --all-files passes, gersemi included.