`Generic` instance with `omitNothingFields = True` is very slow

There seems to be exponential time complexity with `genericToEncoding defaultOptions {omitNothingFields = True}`, although this seems to depend on the ghc version used. Consider the following code (which has been somewhat minimised, but still depends on a fair bit of aeson)
```haskell
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE DerivingStrategies #-}

module Main (main) where

import Data.Aeson.Types.ToJSON (
ToJSON(toEncoding,toJSON),
genericToEncoding,
)
import Data.Aeson.Types.Internal (
defaultOptions,
omitNothingFields,
)
import Data.Aeson.Encoding.Internal (encodingToLazyByteString)
import GHC.Generics (Generic)
import System.Environment (getArgs)

import qualified Data.ByteString.Lazy as L

data Tree
= Node () [Tree]
deriving stock (Show, Generic)

instance ToJSON Tree where
toEncoding = genericToEncoding defaultOptions {omitNothingFields = True}

tree' :: Int -> Tree
tree' 0 = Node () []
tree' n = Node () [tree' $ n-1]

main :: IO ()
main = do
[n'] <- getArgs
let n = read n'
putStrLn "about to print tree"
let tree = tree' n
print $ tree
putStrLn "about to ToJSON tree"
print $ toJSON tree
putStrLn "about to encode tree"
print $ encode tree
putStrLn "done"

---- From aeson

encode :: (ToJSON a) => a -> L.ByteString
encode = encodingToLazyByteString . toEncoding
```

I get results such as the following with ghc 9.2.7
| Command (with ghc 9.2.7) | Mean [ms] | Min [ms] | Max [ms] | Relative |
|:---|---:|---:|---:|---:|
| `cabal run -O1 aeson-slow -- 1` | 53.5 ± 0.1 | 53.4 | 53.9 | 1.00 ± 0.00 |
| `cabal run -O1 aeson-slow -- 2` | 53.5 ± 0.0 | 53.4 | 53.6 | 1.00 ± 0.00 |
| `cabal run -O1 aeson-slow -- 3` | 53.5 ± 0.1 | 53.4 | 53.9 | 1.00 ± 0.00 |
| `cabal run -O1 aeson-slow -- 4` | 53.5 ± 0.0 | 53.4 | 53.6 | 1.00 ± 0.00 |
| `cabal run -O1 aeson-slow -- 5` | 53.5 ± 0.1 | 53.4 | 53.9 | 1.00 ± 0.00 |
| `cabal run -O1 aeson-slow -- 6` | 53.5 ± 0.0 | 53.3 | 53.6 | 1.00 ± 0.00 |
| `cabal run -O1 aeson-slow -- 7` | 53.5 ± 0.1 | 53.3 | 54.0 | 1.00 ± 0.00 |
| `cabal run -O1 aeson-slow -- 8` | 53.5 ± 0.1 | 53.3 | 54.0 | 1.00 ± 0.00 |
| `cabal run -O1 aeson-slow -- 9` | 53.4 ± 0.1 | 53.3 | 53.6 | 1.00 |
| `cabal run -O1 aeson-slow -- 10` | 54.0 ± 2.4 | 53.2 | 64.0 | 1.01 ± 0.05 |
| `cabal run -O1 aeson-slow -- 11` | 63.6 ± 0.2 | 63.4 | 64.3 | 1.19 ± 0.00 |
| `cabal run -O1 aeson-slow -- 12` | 63.6 ± 0.2 | 63.3 | 64.4 | 1.19 ± 0.00 |
| `cabal run -O1 aeson-slow -- 13` | 63.6 ± 0.2 | 63.4 | 64.4 | 1.19 ± 0.00 |
| `cabal run -O1 aeson-slow -- 14` | 71.5 ± 4.2 | 63.2 | 74.9 | 1.34 ± 0.08 |
| `cabal run -O1 aeson-slow -- 15` | 82.0 ± 3.7 | 73.2 | 84.0 | 1.53 ± 0.07 |
| `cabal run -O1 aeson-slow -- 16` | 103.5 ± 0.1 | 103.4 | 103.9 | 1.94 ± 0.00 |
| `cabal run -O1 aeson-slow -- 17` | 143.4 ± 0.0 | 143.4 | 143.5 | 2.68 ± 0.00 |
| `cabal run -O1 aeson-slow -- 18` | 226.5 ± 4.8 | 223.2 | 233.6 | 4.24 ± 0.09 |
| `cabal run -O1 aeson-slow -- 19` | 391.6 ± 15.6 | 383.4 | 434.0 | 7.33 ± 0.29 |
| `cabal run -O1 aeson-slow -- 20` | 722.9 ± 12.0 | 713.9 | 753.9 | 13.53 ± 0.22 |
| `cabal run -O1 aeson-slow -- 21` | 1382.9 ± 14.5 | 1373.5 | 1413.9 | 25.87 ± 0.27 |
| `cabal run -O1 aeson-slow -- 22` | 2720.9 ± 40.5 | 2674.2 | 2774.0 | 50.91 ± 0.76 |
| `cabal run -O1 aeson-slow -- 23` | 5379.8 ± 49.2 | 5304.0 | 5464.0 | 100.65 ± 0.93 |
| `cabal run -O1 aeson-slow -- 24` | 10575.9 ± 32.6 | 10523.8 | 10613.9 | 197.87 ± 0.68 |
| `cabal run -O1 aeson-slow -- 25` | 21091.9 ± 54.6 | 21033.8 | 21203.5 | 394.61 ± 1.18 |
| `cabal run -O1 aeson-slow -- 26` | 42325.9 ± 264.1 | 41984.1 | 42673.9 | 791.89 ± 5.08 |

Note that this seems rather dependent on the specific ghc version used -- I don't know whether this implies that there is a ghc regression/performance fix and this is really an upstream issue, or whether it means that `aeson` relies on some optimization firing and that this can be unreliable (and if it is this second option, I don't know if it is possible to make it more reliable). Running a sweep over different ghc versions I see the following
| GHC version | Mean [ms] | Min [ms] | Max [ms] | Relative |
|:---|---:|---:|---:|---:|
| GHC 8.10.7 | 1.0 ± 0.2 | 1.0 | 3.8 | 1.03 ± 0.19 |
| GHC 9.0.2 | 1.0 ± 0.0 | 1.0 | 1.5 | 1.00 |
| GHC 9.2.4 | 40564.2 ± 125.1 | 40362.9 | 40783.3 | 40655.26 ± 1458.36 |
| GHC 9.2.5 | 39164.4 ± 86.0 | 38997.4 | 39267.6 | 39252.38 ± 1405.47 |
| GHC 9.2.6 | 39244.7 ± 81.5 | 39111.9 | 39365.8 | 39332.87 ± 1408.07 |
| GHC 9.2.7 | 38837.3 ± 141.0 | 38603.0 | 39147.1 | 38924.50 ± 1398.27 |
| GHC 9.4.2 | 43628.6 ± 752.3 | 42621.7 | 44991.6 | 43726.59 ± 1735.12 |
| GHC 9.4.3 | 1272.6 ± 12.0 | 1261.6 | 1291.6 | 1275.50 ± 47.14 |
| GHC 9.4.4 | 12.2 ± 0.1 | 11.8 | 12.4 | 12.18 ± 0.45 |
| GHC 9.4.5 | 12.2 ± 0.2 | 11.7 | 12.6 | 12.19 ± 0.46 |