[5.x] Prevent comma completing tags when defining container validation rules

[duncanmcclean]

This pull request fixes an issue with the Taggable fieldtype when it's used for defining an asset container's validation rules, where a comma in a rule completes the tag, which can be frustrating in the context of validation rules.

Fixes #11122.

[jasonvarga]

Thanks but I think the actual solution should be to bring the validation ux over from the field settings. The use of a taggable fieldtype here was just a quick fix.

The validation field could be extracted to a fieldtype and then used in both places.