Allow for regex patterns in custom_name selects

As far as I can tell, the new item model format could act as a replacement for OptiFine's CIT format which would, for a lot of servers, bring a more consistent visual experience.

However, a server which I administrate uses Regex patterns in it's custom resourcepack in order to check if an item's name is similar to a specified string. As such, to match the flexibility of the previously mentioned system, it would be extremely helpful to extend the vanilla's one such that it would allow regex-based data matching when checking for an item's custom name. I feel like it could be also applied more widely to the general checks of strings in order to make the behavior more consistent and flexible, but idk if that would actually be useful.