PHP 8 fixes

[rdohms]

I'm in the process of upgrading our app to PHP8 and ran into a few issues with the DMS Filter bundle. I've written some fixes that work for my use case, I thought I would raise a PR for them in case it would be useful for them to be incorporated?

The following are changed:

Updated filters to support nullable fields

With PHP8 functions such as strip_tags() can throw when a non-string value is provided. I've wrapped the affected function calls in is_string() checks to provide a graceful fallback, and updated the unit tests accordingly. This has allowed me to continue using the filters on fields that are nullable.

Fixed a crash on the RegExp filter

When the unicodeEnabled static property is not set against the RegExp class, the existing null check in the checkUnicodeSupport method would result in an Error being thrown. I've changed the null check for an isset() call to resolve this.

Added Laminas rule/filter

This is to support the move from Zend to Laminas. I've not made any changes to the existing Zend classes for this. If there is another, better solution for this I'm happy to remove the new classes, or indeed make changes to any of the above.

Thanks, Kieran

Moved here so I could fix some styling issues, thanks @kdadler