Stop using ORO Perl5Util for regex matching

It seems to be used by:

• XWiki#createUser to validate the user id
• PropertyClass#validateProperty to validate the value of a property depending on its configured "validationRegExp"

It does not make any sense to me to use perl regex syntax and there is no explanation to why we are doing this.

Also, Jakarta ORO is long deprecated (2010).

The worst is that we publicly expose ORO Perl5Util and Perl5Matcher classes in "com.xpn.xwiki.util.Util", always a pain to notice such reckless APIs...