New MVE_ROT_HCADD (#90/#270 at bit12) and MVE_ROT_CMLA (#0/90/180/270 at
bits 24:23) rotation encodings -- the rotation degrees round-trip
properly (unlike the existing FCMA VCMLA which leaves it unencoded). One
form each with the element-size bits left variable (MVE convention).
Verify round-trips; all rotations byte-exact vs llvm-mc; 600 tests green.
(VMLSV/VMLSVA reduce ops deferred: their format decode-collides with
other MVE encodings given the 4-bit VN_Q vs MVE's 3-bit Qn.)
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