PR #112292 added support for vectors to the integer range inference
interface and analysis, but didn't update the getDestWidth() method.
This caused crashes when trying to infer the ranges of `arith.extsi`
with vector inputs, as the code would try to sign-extend a N-bit value
to a 0-bit one, which would assert and crash.
This commit fixes the issue by adding a getElementTypeOrSelf().
616aff126c