Add custom code action kinds for import related code actions

[berberman]

Closes #1556

Suggestions are welcome! /cc @isovector

Several examples:

Code Action Title	Before	After	Code Action Kind
Add stuffA to the import list of ModuleA	import ModuleA (stuffB)	import ModuleA (stuffB, stuffA)	quickfix.import.extend.thing.topLevel
Add A to the import list of ModuleA	import ModuleA ()	import ModuleA (A)	quickfix.import.extend.thing.topLevel
Add A(Constructor) to the import list of ModuleA	import ModuleA (A)	import ModuleA (A (Constructor))	quickfix.import.extend.thing.withParent
import Bar (Bar)		import Bar (Bar)	quickfix.import.new.thing.topLevel
import Bar (Bar(Bar))		import Bar (Bar(Bar))	quickfix.import.new.thing.withParent
import Numeric.Natural		import Numeric.Natural	quickfix.import.new.all
import qualified Data.List.NonEmpty as NE		import qualified Data.List.NonEmpty as NE	quickfix.import.new.qualified

[pepeiborra]

Just a minor nitpick, I would prefer list instead of thing for the imports that extend or create an import list, eg. quickfix.import.extend.list.topLevel and quickfix.import.new.list.toplevel

[isovector]

This is marvelous, thanks so much!

[pepeiborra]

@berberman we should document these names in the read me and add instructions on how to use them

[berberman]

Yeah, and I think we should document all ghcide code actions in some place

[michaelpj]

👍 for documenting all these as they come up.

One thing that occurs to me with the naming: it would be nice if the kind and the message sort of had the same structure and terminology? Let me show what I mean:

kind	current	suggestion
quickfix.import.extend.list.topLevel	Add stuffA to the import list of ModuleA	Import: extend the import list of ModuleA with the top-level entity stuffA
quickfix.import.extend.list.withParent	Add A(Constructor) to the import list of ModuleA	Import: extend the import list of ModuleA with the entity Constructor and its parent A
quickfix.import.new.thing.topLevel	import Bar (Bar)	Import: add a new import importing the top-level entity Bar

etc.

At the moment there's a sort of implicit translation of terminology that users have to do: "add to import list" -> "extend"; "" -> "create a new import"; "top-level" and "withParent" aren't used in those ways.

[pepeiborra]

@berberman we are very close to having full import management on save, the main thing missing is "remove redundant import", which did not get a custom kind in this PR.