Add lazy ST monad

[konsumlamm]

Add Control.Monad.ST.Lazy, Control.Monad.ST.Lazy.Unsafe, Control.Monad.ST.Strict, Data.STRef.Lazy, Data.STRef.Strict.

I used primPerformIO to achieve the laziness required for lazy ST.

[konsumlamm]

I marked this as a draft because I noticed that GHC has a test case for lazy ST, which currently fails: https://gitlab.haskell.org/ghc/ghc/-/blob/master/libraries/base/tests/lazySTexamples.hs.

[augustss]

I won't merge until you've tested more.

[konsumlamm]

I rewrote the lazy ST implementation to use State s -> (a, State s), like in the GHC version. The test from GHC's test suite now passes.

[konsumlamm]

It turns out now lazyToStrictST is incorrect, for example

import Control.Monad.ST as S
import Control.Monad.ST.Lazy (lazyToStrict)
import Data.STRef.Lazy as L

main :: IO ()
main = print $ S.runST $ do
  ref <- lazyToStrictST $ L.newSTRef 0
  let action = lazyToStrictST $ L.modifySTRef ref (+ 1)
  action
  action
  lazyToStrictST $ L.readSTRef ref

prints 1, even though it should print 2.