Not guarding against preceding \0 when interpolating into a character class

[slevithan]

RegExp.make`[\0${0}]` returns /[\00]/, which is equivalent to /\0/. The same problem occurs with other interpolated digits.

The correct output should allow it to match a literal '0', similar to how RegExp.make correctly guards against a preceding \0 when interpolating outside of a character class.

I have a working implementation of this in regex, which returns /[\u{0}0]/v.