File and directory helpers on std::filesystem; mkdir() without the shell (#323) (4.2.31)

[ddehilster]

Stage 1 of #323: the file and directory helpers move to std::filesystem. Moving them turned up real bugs.

NLP++ mkdir() (security + correctness). It built a shell command mkdir PATH and ran it with system(). Checked against 4.2.18 on Windows:

• mkdir(G("$apppath") + "/made/plain") made nothing, because cmd reads /made as a switch. It still returned 1.
• mkdir(base + "/x & echo pwned > pwned_323.txt") ran the echo and wrote the file.
• A path with spaces broke.
• It returned 1 whatever happened.

It now uses create_directories and returns whether the directory exists afterwards. Parent folders are made, and an existing folder returns 1. This applies to the interpreter and the compiled runtime.

dir_exists / make_dir / rm_dir in lite/mach.cpp were wrapped in #ifndef LINUX. On Linux and macOS, dir_exists was always true and make_dir/rm_dir did nothing. nlp.cpp relies on these for output and log folders.

kbdumptree() shelled out to cat on Linux and macOS. Every platform now concatenates in C++. It also closes the three part files first: they were read while still open, so their last buffered lines could be missing. The dump is byte-identical to 4.2.18's on Windows.

Also on std::filesystem: prim make_dir/rm_dir, file_size, file_exists (a directory no longer counts as an existing file on Linux), and nlp_engine's stat/mkdir/CreateDirectory.

Left alone on purpose:

• the NLP++ system() builtin and the Python pass (shell use is their job);
• dead Windows build paths (msdev, kb_release.bat, _OLDWAY_);
• the third-party tagger in lextagger.cpp.

Tests:

• New fixture tests/fs-ops with CI steps on Windows and Linux. It checks:
  • mkdir with plain, spaces, nested and existing paths, and that each folder exists;
  • that no pwned_323.txt appears;
  • that the kbdumptree dump holds the concept and attribute and ends with quit.
• Local: 46/47 CI steps pass. The compiled-bridge step needs $GITHUB_WORKSPACE and always fails locally.
• Full English Test: unchanged.
• 20 analyzers × 21 inputs against 4.2.18: 0 differences.
• The compiled fixture gives the same output as the interpreter.

Docs: a visualtext-files PR for the mkdir page follows. Batched: don't tag yet.

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