Add Random.map simplifications

[lue-bird]

Random.map identity generator
--> generator

Random.map (always a) generator
--> Random.constant a

-- not in summary
Random.map << always
--> Random.map

Random.map f (Random.constant x)
--> Random.constant (f x)

-- not in summary
Random.map f << Random.constant
--> Random.constant << f

part of https://github.com/jfmengels/elm-review-simplify/issues/109

Some comments

• The generalized checks for map f (pure x) and map identity are also now re-used for existing Maybe.map, Result.map, ... checks
  • they are versatile and pretty: you can for example use them with Ok and map or with Err and mapError
• As an unrelated change, I upgraded elm-syntax to the latest version to make the local tests pass
• I feel like I could do another round of cleanups with better errors for error infos I marked TODO, more performant compositionChecks similar to functionCallChecks, changing ModuleName -> String -> ... to ( ModuleName, String ) -> ... etc
• The amount of tests here kind of went out of hand (and the list isn't even complete). We could (from now on?) combine cases with equivalent/similar output to get a more focused file, slightly faster and less boring test creation, better performance (not that this has been a problem) but also a bit less clear errors. Thoughts?