Follow up to 3bc09c7da5 - remove a fixme I forgot to remove, and add test cases showing remaining work.
Note that scaled vscales show up in vectorized code from a couple of sources:
* Element types smaller than vector block size (i.e. everything under i64)
* Unrolling
* LMUL > 1
The largest scaling we can currently have is 256 (e8 in every possible vector register). More practically useful scales are in the 2-16 range.