Switch from Data.BigInt to JS.BigInt

[klntsky]

• https://github.com/purescript-contrib/purescript-bigints that uses big-integer NPM package is deprecated
• https://github.com/purescript-contrib/purescript-js-bigints uses native bigints

[kozross]

I don't think this is possible without a compiler upgrade. Even on 1.2.0 (which is a year old), I get the following:

[1/3 ModuleNotFound] .spago/js-bigints/a23c0ec1b3cb6c8468202221f51b162c2aa81516/src/Js/BigInt/BigInt.purs:23:1

  23  import Data.Reflectable (class Reflectable, reflectType)
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  
  Module Data.Reflectable was not found.
  Make sure the source file exists, and that it has been provided as an input to the compiler.

This is a module that was introduced in a more recent version of Purescript than the one we run.

[klntsky]

Sorry @kozross, forgot to mention it should be done on top of #1521

[klntsky]

#1521