Cmake: add defconfig preprocess capability in Cmake build environment(recursively expand #include)

Add:
    cmake/nuttx_process_config.cmake
    tools/process_config.py

    Update nuttx/CMakeLists.txt to call process_config defined ini
    nuttx_process_config.cmake to process defconfig before actually using it

cmake/nuttx_process_config.cmake

@@ -0,0 +1,48 @@
+# ##############################################################################
+# cmake/nuttx_process_config.cmake
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more contributor
+# license agreements.  See the NOTICE file distributed with this work for
+# additional information regarding copyright ownership.  The ASF licenses this
+# file to you under the Apache License, Version 2.0 (the "License"); you may not
+# use this file except in compliance with the License.  You may obtain a copy of
+# the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+# License for the specific language governing permissions and limitations under
+# the License.
+#
+# ##############################################################################
+
+function(process_config OUTPUT INPUT)
+  set(options)
+  set(oneValueArgs)
+  set(multiValueArgs INCLUDE_PATHS)
+  cmake_parse_arguments(PARSE_ARGV 2 PROCESS_INCLUDES "${options}"
+                        "${oneValueArgs}" "${multiValueArgs}")
+
+  find_package(Python3 REQUIRED COMPONENTS Interpreter)
+
+  set(include_args "")
+  foreach(path IN LISTS PROCESS_INCLUDES_INCLUDE_PATHS)
+    list(APPEND include_args "${path}")
+  endforeach()
+
+  message(STATUS "Processing includes: ${INPUT} → ${OUTPUT}")
+  execute_process(
+    COMMAND ${Python3_EXECUTABLE} ${CMAKE_SOURCE_DIR}/tools/process_config.py
+            ${OUTPUT} ${INPUT} ${include_args}
+    RESULT_VARIABLE result
+    OUTPUT_VARIABLE out
+    ERROR_VARIABLE err)
+
+  if(NOT result EQUAL 0)
+    message(FATAL_ERROR "Failed to process includes:\n${err}")
+  endif()
+endfunction()