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/GetBinaryDeps.cmake

@@ -0,0 +1,43 @@
+# This is similar to the build recipes, but instead downloads a third party
+# binary and installs it under the DEPS_PREFIX.
+# The INSTALL_COMMAND is executed in the folder where downloaded files are
+# extracted and the ${DEPS_INSTALL_DIR} holds the path to the third-party
+# install root.
+function(GetBinaryDep)
+  cmake_parse_arguments(_gettool
+    "BUILD_IN_SOURCE"
+    "TARGET"
+    "INSTALL_COMMAND"
+    ${ARGN})
+
+  if(NOT _gettool_TARGET OR NOT _gettool_INSTALL_COMMAND)
+    message(FATAL_ERROR "Must pass INSTALL_COMMAND and TARGET")
+  endif()
+
+  string(TOUPPER "${_gettool_TARGET}_URL" URL_VARNAME)
+  string(TOUPPER "${_gettool_TARGET}_SHA256" HASH_VARNAME)
+  set(URL ${${URL_VARNAME}})
+  set(HASH ${${HASH_VARNAME}})
+  if(NOT URL OR NOT HASH )
+    message(FATAL_ERROR "${URL_VARNAME} and ${HASH_VARNAME} must be set")
+  endif()
+
+  ExternalProject_Add(${_gettool_TARGET}
+    PREFIX ${DEPS_BUILD_DIR}
+    URL ${URL}
+    DOWNLOAD_DIR ${DEPS_DOWNLOAD_DIR}
+    DOWNLOAD_COMMAND ${CMAKE_COMMAND}
+      -DPREFIX=${DEPS_BUILD_DIR}
+      -DDOWNLOAD_DIR=${DEPS_DOWNLOAD_DIR}
+      -DURL=${URL}
+      -DEXPECTED_SHA256=${HASH}
+      -DTARGET=${_gettool_TARGET}
+      -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 ${CMAKE_COMMAND} -E make_directory ${DEPS_INSTALL_DIR}/bin
+    COMMAND "${_gettool_INSTALL_COMMAND}")
+  list(APPEND THIRD_PARTY_DEPS ${__gettool_TARGET})
+endfunction()