feat: Add several missing functions and fix file_exists error

[laurensschuitemaker]

Each pull request should address a single issue and have a meaningful title.

Description
Explain what you have changed, and why.

Checklist:

• Component(s) with PHPDocs
• Unit testing, with >85% coverage
• Document updated
• Conforms to coding standard

---------Remove from here down in your description----------

Notes

• Pull requests must be in English
• If the PR solves an issue, reference it with a suitable verb and the issue number
  (e.g. fixes 12345)
• Unsolicited pull requests will be considered, but there is no guarantee of acceptance
• Pull requests should be from a feature branch in the contributor's fork of the repository
  to the develop branch of the project repository

[kenjis]

What is the file_exists error?

Could you write test code?

[kenjis]

I updated the 1.x branch, and now all GitHub Action checks pass.
Please update your PR branch with git rebase.