[REQ] Update pattern handling to disallow /pattern/ and /pattern/flags

[spacether]

Is your feature request related to a problem? Please describe.

Update pattern handling to disallow /pattern/ and /pattern/flags

Describe the solution you'd like

Those inputs should be disallowed because the 2020-12 json schema spec describes regexes as the pattern value only and does not include slashes and flags

This was discussed in the json schema slack group

Describe alternatives you've considered

Additional context