feat(asm): encode the arm64 register-offset addressing forms

Assisted-by: GLM 5.3 Flash

verify/arm64_groundtruth_test.go

@@ -37,6 +37,7 @@ func TestGroundTruthARM64(t *testing.T) {
 		"../testdata/verify/atomics_arm64.s",
 		"../testdata/verify/qmov_arm64.s",
 		"../testdata/verify/splits_arm64.s",
+		"../testdata/verify/regoffset_arm64.s",
 		"../testdata/verify/crypto_arm64.s",
 		"../testdata/verify/integer_arm64.s",
 		"../testdata/verify/simd_arm64.s",