Reports back references that will not be resolvable at runtime.
This means that the back reference can never match anything.
A back reference will not be resolvable when the group is defined after the back reference,
or if the group is defined in a different branch of an alternation.
Example of a group defined after its back reference:
\1(abc)
Example of a group and a back reference in different branches:
a(b)c|(xy)\1z
New in 2022.1