Table lookup TBL/TBX (.8b/.16b, single-register table) and the multi-
register structured load/store LD2/LD3/LD4, ST2/ST3/ST4 plus load-and-
replicate LD1R/LD2R/LD3R/LD4R (.16b). Following the existing LD1/ST1
convention: the register list is encoded by its first register, with the
list length + arrangement fixed in the bits. All 13 representative forms
byte-exact vs llvm-mc and decode-clean; 461 tests green.
(The single-lane _LANE variants need the Q:S:size lane-index split and
are left for a follow-up.)
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