Adds support for multiple app copies in rseq mangling finalization's search for labels to fill in code cache PC's.
Adds support for multiple rseq regions in one fragment_t by expanding the stored rseq_cs per fragment to become a list.
Adds "-trace_after_instrs 5K" to the tool.drcacheoff.rseq test to exercise rseq with drbbdup.
Augments the attach/detach api.rseq test to use drmemtrace, which with the forthcoming #2039 (closed) mode switches also hits this multi-rseq case.
Fixes #5659 (closed)