Add Cats RemoveInstancesImport rule

[armanbilge]

Fixes #7.

Sadly I am out of my depth with this one. Seems that this rule was written with the Scalafix v0 API and I'm not quite sure how to make it work. Perhaps it needs to be rewritten with the v1 API.

[DavidGregory084]

I made a start at porting this one to scalafix v1 API in 82b45b0, but I'm a bit out of my depth as well. I'm not sure how to connect synthetics to their positions in v1, something which the old rule used to determine the scope of the imports it was rewriting.

[DavidGregory084]

I think we can get the synthetics for a given Term by simply calling .synthetics on it, but that doesn't work for e.g. Template, which is a Tree but not a Term.

[TonioGela]

Hey people, I took the liberty of attempting to fix this and apparently I've managed to do that. The only thing I'm not sure about is this change:

  private def catsKernelConversion(symbol: Symbol): Boolean =
-    symbol.value.contains("cats/kernel") && symbol.value.contains("Conversion")
+    symbol.value.contains("cats/kernel") // && symbol.value.contains("Conversion")

I think that this specific predicate was referring to a specific .*Conversion.* object under the cats/kernel package that was containing all the conversions, that is not present anymore (as far as I can tell). I don't know which might be the better choice, maybe symbol.value.contains("cats/kernel/instances") given that all the instances seems to be sitting there?