Switch to using `Data.Vector.Strict` with `VMap`

[teodanciu]

Currently, Data.Vector (Vector) is used for boxed storage in VMap, for example in Snapshots:

data SnapShot = SnapShot
  {  
   ...
  , ssDelegations :: VMap VB VB (Credential Staking) (KeyHash StakePool)
  , ssPoolParams :: VMap VB VB (KeyHash StakePool) StakePoolParams 
  , ssStakePoolsSnapShot :: !(VMap VB VB (KeyHash StakePool) StakePoolSnapShot)
}

Once we switch to vector-0.13.2.0 , we can use Data.Vector.Strict wherever we want to make sure there are no thunks.

The NoThunks instance for Data.Vector.Strict has already been implemented in this PR: #5545.

With the switch, we should also implement the now commented out functions: mapValsKVVector and mapWithKeyKVVector in Data.VMap.KVVector and then switch to them in the respective function map and mapWithKey in the Data.VMap module.