BUG: Locale-independent itk::StringToDouble/Float; remove NumericLocale

itk::StringToDouble and itk::StringToFloat followed the ambient
LC_NUMERIC, so every migrated IO call site parsed "0.878906" as 0
under a decimal-comma locale.

They parse with strtod_l/strtof_l against a cached "C" locale, keeping
the itk::ExceptionObject contract; only overflow throws, as ERANGE
underflow is a valid subnormal or zero. A platform lacking newlocale
and _configthreadlocale fails to compile.

NumericLocale is removed: uselocale() cannot bind the non-_l
std::strtod on macOS 13 libc, and it shipped only in the v6.0b02
beta, so no deprecation shim is required.

Author: hjmjohnson

Modules/Core/Common/CMakeLists.txt

@@ -158,7 +158,7 @@ try_compile(
   ${CMAKE_CURRENT_SOURCE_DIR}/CMake/itkCheckHasSchedGetAffinity.cxx
 )
 
-# Check for thread-local locale functions for NumericLocale
+# Check for thread-safe locale functions (locale-independent parsing in itkStringConvert)
 try_compile(
   ITK_HAS_NEWLOCALE
   ${ITK_BINARY_DIR}

Modules/Core/Common/include/itkNumericLocale.h

@@ -43,6 +43,10 @@ namespace itk
  * `context` describing what was being parsed (e.g.
  * ``"NRRD header field 'sizes'"``) plus the offending input string.
  *
+ * The floating-point helpers parse with an explicit "C" locale, so `.` is the
+ * decimal separator regardless of the ambient `LC_NUMERIC` locale. Underflow to
+ * a subnormal or zero is a valid value; only overflow throws.
+ *
  * **Fixed-width integer return types** are used (`int32_t`, `int64_t`,
  * `uint32_t`, `uint64_t`) rather than the platform-dependent C++
  * spellings (`int`, `long`, `unsigned long`). The C++ Standard only

Modules/Core/Common/include/itkStringConvert.h

@@ -106,7 +106,6 @@ set(
   itkMultipleLogOutput.cxx
   itkMultiThreaderBase.cxx
   itkNumberToString.cxx
-  itkNumericLocale.cxx
   itkNumericTraits.cxx
   itkNumericTraitsCovariantVectorPixel.cxx
   itkNumericTraitsDiffusionTensor3DPixel.cxx