feat: Add getForbiddenFilenames to \OCP\Util and unify filename sanitizing

[susnux]

Some preparations and refactoring for #44963

Summary

• Add a common access to the forbidden filename config (now \OCP\Util::getForbiddenFilenames())
• Cache forbidden filenames and characters, as with 🪟📁📄 Ability to enforce windows compatible file names on the server #44963 the function for calculating those values might be more complex (also the forbidden filenames were already cached on the filesystem class).
• Drop OC_Util::isValidFilename as it was deprecated for a long time, not used anymore and not checking forbidden filenames
• Deprecate \OCP\Files\FileInfo::BLACKLIST_FILES_REGEX as this was not used anywhere (only in the util function but that is also not used anywhere + in the files app, but never enforced on webdav).
• Add the forbidden filenames and forbidden characters to the JS config for frontend validation use

Todo ⚠️ - Needs discussion

• It was never documented but the deny list of files was somewhat case in-sensitive. Document that or make it case-sensitive? (The first is currently done).
• The file name blacklist regex was not enforced anywhere, meaning you can currently upload .fileinfo files. So I dropped it, but should be instead enfore it?

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)