Migrate Map's to HashMap's

[Anton-Latukha]

In Derivation noted a number of Map.fromList . HashMap.toList. This shows that there should be a newtype boundary between those abstractions or none at all.

> hrg 'Data.Map'
./tests/NixLanguageTests.hs
9:import qualified Data.Map                      as Map

./src/Nix/Type/Infer.hs
43:import qualified Data.Map                      as Map

./src/Nix/Type/Env.hs
27:import qualified Data.Map                      as Map

./src/Nix/Effects/Derivation.hs
19:import qualified Data.Map.Strict               as Map

./main/Main.hs
17:import qualified Data.Map                      as Map

As seen - the additional point is they are mostly lazy maps.

Most of the code overall uses HashMap, the only uses of Map are in Derivation, and in the inference infrastructure. The migration in Derivation seems beneficial. In the inference, Map.Lazy is currently used in substitutions & typing environments, typing environment probably can get big.

Looking at https://github.com/haskell-perf/dictionaries, HashMap is still preferable in the majority of cases. At least the case in Derivation suggest to stick to HashMap there.

[layus]

There is the slight issue that HashMap are not sorted. However, Nix specifies that attribute sets should be sorted. It is very important for derivations, because the order influences the store path hash.