Embed a Python file in a C++17 header via CMake configure_file

To ship a script (e.g. gdb pretty-printers for .debug_gdb_scripts) inside a C++17 binary while keeping it a real .py file with tooling, file(READ) it into a variable and configure_file a template like inline const char* text = R"py(@VAR@)py"; with @ONLY into a generated include dir. Two gotchas: CMake does not track files read with file(READ), so add set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS path.py) or edits won't regenerate the header; and guard against the raw-string closing delimiter appearing in the file with if(VAR MATCHES "\\)py\"") message(FATAL_ERROR ...). configure_file substitution isn't recursive, so @...@ inside the file's content is safe.