Replace abandoned composer package 'webmozart/path-util'

[hkorik]

Motivation
Fixes #4669 . As outlined in the projects deprecation notice this should be replaced with the symfony filesystem component.

Proposed changes
Replaces the method used from the Path utility from webmozart/path-util with a replacement method from the symfony/filesystem component. Removes the composer direct dependency on the abandoned project.

Testing steps
Ensure the blt internal:add-to-project command successfully adds custom blt related files to the expected .gitignore file within the configured project repo.root directory.

[danepowell]

Unfortunately, I don't think we can do this until Drupal 9 is EOL, since Drupal 9 requires Symfony 4 and the path utilities were only added to Symfony 5.

[gaards]

We are about a week away from D9 EOL, could this PR now be revisited/reopened/recreated?

https://www.drupal.org/about/core/policies/core-release-cycles/schedule

[danepowell]

Yes, we will revisit this in the near future

[danepowell]

Superseded by #4706

@hkorik thanks for your PR; if you really want credit for this commit, let me know and I'll try to cherry-pick it into the new PR.