Style/RedundantRegexpEscape should register and offence for escaped hypens in character groups when a hypen is the first/last character

[Earlopain]

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

Consider the following regexes:

unescaped1 = /[0-9-]/
escaped1   = /[0-9\-]/

unescaped2 = /[-0-9]/
escaped2   = /[\-0-9]/

All 4 match numbers 0 through 9 and -. It is not neccesary to escape - when it is the first or last character in the group since there is no ambiguity about it. Either the user mistyped or it is intended like this. Regardless of that, the backslash is redundant.

Describe the solution you'd like

Rubocop should register an offence for escaped hypens in character groups when the hypen is either the first or last character.