`regexp/prefer-d`: Add an option for whole `\d`s

[RunDevelopment]

Description
I think that the range 0-9 can be more readable than \d in some situations. E.g. [0-9a-f] vs [\da-f].

I think we should an option that makes it so that only whole character classes that are equal to \d or \D are reported. So [0-9] will be reported but [0-9a-f] won't.

What do you think @ota-meshi?

[ota-meshi]

I personally think that worth this rule to unify those writing styles.

If we add an option to allow [0-9a-f] to the rule, I think the rule should report [\da-f].