[EXPERIMENTAL] Make NilClass#to_s, TrueClass#to_s and FalseClass#to_s return a frozen String
* Always the same frozen String for each of these values. * Avoids extra allocations whenever calling these 3 methods. * See [Feature #16150]
[EXPERIMENTAL] Make NilClass#to_s, TrueClass#to_s and FalseClass#to_s return a frozen String