Manually encoding and decoding logical immediates is error-prone.
Using ORRI2R and friends lets us avoid doing the work manually,
but in exchange, there is a runtime performance penalty. It's
probably rather small, but still, it would be nice if we could
let the compiler do the work at compile-time. And that's exactly
what this commit does, so now I have no excuse for trying to
manually write logical immediates anymore.