ENH: Adding function to help generate __init__.pyi

An interface file can be used to provide introspection
into a libary.

```
python3 ${ITK_BUILD_DIR}/Wrapping/Generators/Python/itk_generate_pyi.py
```

The .pyi file provides hints to IDE's so that
they can help with dynamic introspection
during code development.

The itk/__init__.py file 'lifts symbols' from
the individial modules into the itk package namespace
in a dynamic way that is not visible by many IDE's,
the explicit generation of an interface file can
provide the necessary information needed to assist
development.

Wrapping/Generators/Python/CMakeLists.txt

@@ -152,10 +152,9 @@ if(NOT EXTERNAL_WRAP_ITK_PROJECT)
     itk/support/itkHelpers
     itk/support/itkInitHelpers
     itk/__init__
-    itk/itkInitHelpers
+    itk_generate_pyi # A utility function used to generate the intreface file
     )
   # Done listing files.
-
   # Now copy these files if necessary.
 
   set(ITK_WRAP_PYTHON_INSTALL_FILES )
@@ -1000,5 +999,5 @@ add_custom_command(OUTPUT ${ITK_WRAP_PYTHON_ROOT_BINARY_DIR}/itk/__init__.pyi
     COMMAND ${Python3_EXECUTABLE} ${ITK_WRAP_PYTHON_ROOT_BINARY_DIR}/itk_generate_pyi.py
     DEPENDS ${ITK_WRAP_PYTHON_FILES} ${WRAPPER_LIBRARY_NAME}Swig
     WORKING_DIRECTORY ${ITK_WRAP_PYTHON_ROOT_BINARY_DIR}
-    COMMENT "Building pythong type interface file itk/__init__.pyi for the itk package"
+    COMMENT "Building python type interface file itk/__init__.pyi for the itk package"
 )

Wrapping/Generators/Python/itk_generate_pyi.py

@@ -0,0 +1,85 @@
+from typing import List, Any
+import inspect
+import importlib
+import sys
+
+try:
+    # First attempt using convention of build directory
+    from pathlib import Path
+
+    wrap_itk_pth: Path = Path(__file__).parent / "WrapITK.pth"
+
+    if not wrap_itk_pth.is_file():
+        print(
+            "ERROR: itk_generate_pyi.py must be run in the same directory as the WrapITK.pth file"
+        )
+
+    with open(wrap_itk_pth, "r") as fid:
+        itk_module_paths = [
+            itk_module_path.strip() for itk_module_path in fid.readlines()
+        ]
+        for pp in itk_module_paths:
+            if not pp.startswith("#"):
+                sys.path.append(pp)
+    import itkConfig
+except:
+    # Second attempt on the standard path
+    import itkConfig
+
+itkConfig.LazyLoading = False
+itkConfig.DumpInterfaces = True
+
+requested_module_name = "itk"
+requested_module = importlib.import_module(requested_module_name)
+
+# Can not dump complete .pyi interface file if LazyLoading is ued
+class ITKSignaturesList:
+    """
+    A pure static class to manage dumping a .pyi file for
+    the itk_module.
+    """
+
+    _itk_namespace_list: List[str] = []
+    _broken_introspection_signatures: List[str] = ["echo", "image", "string", "str"]
+
+    @staticmethod
+    def parse_object(obj_name: str, obj: Any):
+        # builtin classes do not have introspection signatures.
+        if inspect.isbuiltin(obj):
+            return
+        elif obj_name in ITKSignaturesList._broken_introspection_signatures:
+            return
+        elif obj_name.startswith("_"):
+            return
+        elif inspect.isclass(obj):
+            ITKSignaturesList._itk_namespace_list.append(f"class {obj_name}:")
+            methods_exists: bool = False
+            for elem_name, elem_obj in obj.__dict__.items():
+                if inspect.ismethod(elem_obj) or inspect.isfunction(elem_obj):
+                    methods_exists = True
+                    ITKSignaturesList._itk_namespace_list.append(
+                        f"    def {elem_name}{inspect.signature(elem_obj)}: ..."
+                    )
+            if not methods_exists:
+                ITKSignaturesList._itk_namespace_list[-1] += " ..."
+        elif inspect.isfunction(obj):
+            ITKSignaturesList._itk_namespace_list.append(
+                f"def {obj_name}{inspect.signature(obj)}: ..."
+            )
+        # else:
+        #     print(f"{obj_name}: {type(obj)}")
+
+    @staticmethod
+    def dumps(dump_file: str) -> None:
+        with open(dump_file, "w") as fid:
+            for ln in ITKSignaturesList._itk_namespace_list:
+                fid.write(f"{ln}\n")
+
+
+# Now iterate through all module items and print of signatures
+# of the objects collected.  The generation of a .pyi file
+# allows IDE's and other tools to do better introspection
+all_items = list(requested_module.__dict__.items())
+for k, v in all_items:
+    ITKSignaturesList.parse_object(k, v)
+ITKSignaturesList.dumps(requested_module.__file__ + "i")