ddev: ddev composer still doesn't quite do symlinks that result in proper behavior

Describe the bug

In v1.4.0 we introduced ddev composer, whose intent is to provide in-container predictable behavior, especially on Windows.

Inside the linux containers, creating a symlink appears to work (ln -s), and most linux commands respect it.

Sadly, php does not respect the “XSym” file that is created. So if you try to read a symlink with PHP, you’ll get the contents of the XSym file, not the contents of the target file.

To Reproduce

• On Windows, in the container, on the mounted NTFS volume, create a file named README.md with the contents This is just a simple readme for testing purposes.
• create a symlink to the README.md. For example, ln -s README.md mysymlink.md
• Read the file with cat. It will work fine. cat mysymlink.md will result in the proper output (the content of README.md).
• Read the file with PHP instead, using this script:

<?php

if ($fh = fopen('mysymlink.md', 'r')) {
    while (!feof($fh)) {
        $line = fgets($fh);
        echo $line;
    }
    fclose($fh);
}

Expected behavior

php should read the target file instead. Which is what it does if you create a proper symlink on the Windows host:

• Developer mode must be turned on on the host (See https://blogs.windows.com/buildingapps/2016/12/02/symlinks-windows-10/)
• In git-bash export MSYS=winsymlinks:nativestrict
• ln -s README.md mysymlink.md
• Read the file with the same php script inside the container. It gets the correct content.

Additional context

• @ohader notes that this project creates unusable symlinks even when run inside the container: https://github.com/HofUniversityIndieOne2018/red-cross-project
• @ohader has also written a script (to be run on the host, after composer install, https://gist.github.com/ohader/f4b792e0bb99e79efe75605008ce4a0d#file-use-native-symlinks-sh, to relink XSym as “junction symlinks”
• This old forum post gives some context about “junction links”
• This docker-for-win issue seems to deal with the same problems: https://github.com/docker/for-win/issues/137