Add list of exception patterns to Style/NumericLiterals

[dmke]

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

In a current project, I need to handle identification numbers, which follow the format <2 digit classification> <2 digit region id> <4 digit running number> <1 digit checksum> ("Institutionskennzeichen", "IK number"), for example 112233334

Describe the solution you'd like

I'd like to format them in code as 11_22_3333_4, but the Style/NumericLiterals cop wants me to format them as 112_233_334, which is nonsensical.

I also don't want to lose the warnings for ordinary numbers, where grouping the digits in triplets is desirable.

Describe alternatives you've considered

• Strict: false (default) takes offense with 11_22_3333_4
• AllowedNumbers: [...] does not scale
• Enabled: false is my current workaround

Additional context

It would be nice to define (a list of) allowed patterns, for example:

Style/NumericLiterals:
  AllowedPatterns:     # list of exceptions, like AllowedNumbers
  - xx_xx_xxxx_x       # either using placeholders
  - \d\d_\d\d_\d{4}_\d # or using regexp

I'm not sure if there's precedent for either placeholders or regular expressions in other cops. Maybe there are better alternatives to declare such exceptions.