[LegalizeTypes] When promoting BITREVERSE/BSWAP don't take the shift amount into...

[LegalizeTypes] When promoting BITREVERSE/BSWAP don't take the shift amount into account when determining the shift amount VT.

If the target's preferred shift amount VT can't hold any shift
amount for the promoted VT, we should use i32. The specific shift
amount shouldn't matter. The type will be adjusted later when the
shift itself is type legalized. This avoids an assert in getNode.

Fixes PR43820.