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/BuildLibtermkey.cmake

@@ -0,0 +1,57 @@
+if(WIN32)
+ExternalProject_Add(libtermkey
+  PREFIX ${DEPS_BUILD_DIR}
+  URL ${LIBTERMKEY_URL}
+  DOWNLOAD_DIR ${DEPS_DOWNLOAD_DIR}/libtermkey
+  DOWNLOAD_COMMAND ${CMAKE_COMMAND}
+  -DPREFIX=${DEPS_BUILD_DIR}
+  -DDOWNLOAD_DIR=${DEPS_DOWNLOAD_DIR}/libtermkey
+  -DURL=${LIBTERMKEY_URL}
+  -DEXPECTED_SHA256=${LIBTERMKEY_SHA256}
+  -DTARGET=libtermkey
+  -DUSE_EXISTING_SRC_DIR=${USE_EXISTING_SRC_DIR}
+  -P ${CMAKE_CURRENT_SOURCE_DIR}/cmake/DownloadAndExtractFile.cmake
+  CONFIGURE_COMMAND ${CMAKE_COMMAND} -E copy
+    ${CMAKE_CURRENT_SOURCE_DIR}/cmake/libtermkeyCMakeLists.txt
+      ${DEPS_BUILD_DIR}/src/libtermkey/CMakeLists.txt
+    COMMAND ${CMAKE_COMMAND} ${DEPS_BUILD_DIR}/src/libtermkey
+      -DCMAKE_INSTALL_PREFIX=${DEPS_INSTALL_DIR}
+      # Pass toolchain
+      -DCMAKE_TOOLCHAIN_FILE=${TOOLCHAIN}
+      -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
+      # Hack to avoid -rdynamic in Mingw
+      -DCMAKE_SHARED_LIBRARY_LINK_C_FLAGS=""
+      -DCMAKE_GENERATOR=${CMAKE_GENERATOR}
+      -DCMAKE_GENERATOR_PLATFORM=${CMAKE_GENERATOR_PLATFORM}
+      -DUNIBILIUM_INCLUDE_DIRS=${DEPS_INSTALL_DIR}/include
+      -DUNIBILIUM_LIBRARIES=${DEPS_LIB_DIR}/${CMAKE_STATIC_LIBRARY_PREFIX}unibilium${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()
+find_package(PkgConfig REQUIRED)
+
+ExternalProject_Add(libtermkey
+  PREFIX ${DEPS_BUILD_DIR}
+  URL ${LIBTERMKEY_URL}
+  DOWNLOAD_DIR ${DEPS_DOWNLOAD_DIR}/libtermkey
+  DOWNLOAD_COMMAND ${CMAKE_COMMAND}
+  -DPREFIX=${DEPS_BUILD_DIR}
+  -DDOWNLOAD_DIR=${DEPS_DOWNLOAD_DIR}/libtermkey
+  -DURL=${LIBTERMKEY_URL}
+  -DEXPECTED_SHA256=${LIBTERMKEY_SHA256}
+  -DTARGET=libtermkey
+  -DUSE_EXISTING_SRC_DIR=${USE_EXISTING_SRC_DIR}
+  -P ${CMAKE_CURRENT_SOURCE_DIR}/cmake/DownloadAndExtractFile.cmake
+  CONFIGURE_COMMAND ""
+  BUILD_IN_SOURCE 1
+  BUILD_COMMAND ""
+  INSTALL_COMMAND ${MAKE_PRG} CC=${DEPS_C_COMPILER}
+                              PREFIX=${DEPS_INSTALL_DIR}
+                              PKG_CONFIG_PATH=${DEPS_LIB_DIR}/pkgconfig
+                              CFLAGS=-fPIC
+                              LDFLAGS+=-static
+                              ${DEFAULT_MAKE_CFLAGS}
+                              install)
+endif()
+
+list(APPEND THIRD_PARTY_DEPS libtermkey)