report the trailing replacement in ReplacementsFinder

[rootvector2]

ReplacementsFinder flushes its pending deletions and insertions only from visitKeepCommand and EditScript.visit gives the visitor no end-of-script signal, so any script that ends on a modification silently drops that last replacement (abc to abd reports nothing at all, and with no shared element the handler is never called once); EditScript.visit now reports the end of the script through a new CommandVisitor.visitEndOfScript default no-op that ReplacementsFinder overrides to hand over the trailing block, found by replaying the reported replacements back onto the first sequence over randomized pairs.

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