build: rename build-related dirs

Problem:
Dirs "config", "packaging", and "third-party" are all closely related
but this is not obvious from the layout. This adds friction for new
contributors.

Solution:
- rename config/ to cmake.config/
- rename test/config/ to test/cmakeconfig/ because it is used in Lua
  tests: require('test.cmakeconfig.paths').
- rename packaging/ to cmake.packaging/
- rename third-party/ to cmake.deps/ (parallel with .deps/)

cmake.deps/cmake/BuildGettext.cmake

@@ -0,0 +1,37 @@
+if(MSVC)
+
+  ExternalProject_Add(gettext
+    PREFIX ${DEPS_BUILD_DIR}
+    URL ${GETTEXT_URL}
+    DOWNLOAD_DIR ${DEPS_DOWNLOAD_DIR}/gettext
+    DOWNLOAD_COMMAND ${CMAKE_COMMAND}
+      -DPREFIX=${DEPS_BUILD_DIR}
+      -DDOWNLOAD_DIR=${DEPS_DOWNLOAD_DIR}/gettext
+      -DURL=${GETTEXT_URL}
+      -DEXPECTED_SHA256=${GETTEXT_SHA256}
+      -DTARGET=gettext
+      -DUSE_EXISTING_SRC_DIR=${USE_EXISTING_SRC_DIR}
+      -P ${CMAKE_CURRENT_SOURCE_DIR}/cmake/DownloadAndExtractFile.cmake
+    CONFIGURE_COMMAND ${CMAKE_COMMAND} -E copy
+      ${CMAKE_CURRENT_SOURCE_DIR}/cmake/GettextCMakeLists.txt
+        ${DEPS_BUILD_DIR}/src/gettext/CMakeLists.txt
+      COMMAND ${CMAKE_COMMAND} ${DEPS_BUILD_DIR}/src/gettext
+        -DCMAKE_INSTALL_PREFIX=${DEPS_INSTALL_DIR}
+        # Pass toolchain
+        -DCMAKE_TOOLCHAIN_FILE=${TOOLCHAIN}
+        -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
+        -DCMAKE_GENERATOR=${CMAKE_GENERATOR}
+        -DCMAKE_GENERATOR_PLATFORM=${CMAKE_GENERATOR_PLATFORM}
+        -DLIBICONV_INCLUDE_DIRS=${DEPS_INSTALL_DIR}/include
+        -DLIBICONV_LIBRARIES=${DEPS_LIB_DIR}/${CMAKE_STATIC_LIBRARY_PREFIX}libcharset${CMAKE_STATIC_LIBRARY_SUFFIX}$<SEMICOLON>${DEPS_LIB_DIR}/${CMAKE_STATIC_LIBRARY_PREFIX}libiconv${CMAKE_STATIC_LIBRARY_SUFFIX}
+    BUILD_COMMAND ${CMAKE_COMMAND} --build . --config ${CMAKE_BUILD_TYPE}
+    INSTALL_COMMAND ${CMAKE_COMMAND} --build . --target install --config ${CMAKE_BUILD_TYPE})
+
+else()
+  message(FATAL_ERROR "Trying to build gettext in an unsupported system ${CMAKE_SYSTEM_NAME}/${CMAKE_C_COMPILER_ID}")
+endif()
+
+list(APPEND THIRD_PARTY_DEPS gettext)
+if(USE_BUNDLED_LIBICONV)
+  add_dependencies(gettext libiconv)
+endif()