This change tracks the current offset (number of bytes fed into matchers)
on the top-level RuleEndpointState such that we can compute the relative ending
for matched texts individually.
Additionally, it adds the data_end_offset as a new optional parameter to
signature_match().
This change allows to specify a per signature specific event, overriding
the default signature_match event. It further removes the message
parameter from such events if not provided in the signature.
This also tracks the message as StringValPtr directly to avoid
allocating the same StringVal for every DoAction() call.
Closes#3403
