Refactor GraphQL/UserResovler to use new GlobalID types

.rubocop_todo.yml

@@ -1285,4 +1285,3 @@ Graphql/IDType:
     - 'app/graphql/resolvers/error_tracking/sentry_error_stack_trace_resolver.rb'
     - 'app/graphql/resolvers/snippets_resolver.rb'
     - 'app/graphql/resolvers/user_merge_requests_resolver.rb'
-    - 'app/graphql/resolvers/user_resolver.rb'

app/graphql/resolvers/user_resolver.rb

@@ -6,7 +6,7 @@ module Resolvers
 
     type Types::UserType, null: true
 
-    argument :id, GraphQL::ID_TYPE,
+    argument :id, Types::GlobalIDType[User],
              required: false,
              description: 'ID of the User'
 

doc/api/graphql/reference/gitlab_schema.graphql

@@ -15595,7 +15595,7 @@ type Query {
     """
     ID of the User
     """
-    id: ID
+    id: UserID
 
     """
     Username of the User

doc/api/graphql/reference/gitlab_schema.json

@@ -45088,7 +45088,7 @@
                   "description": "ID of the User",
                   "type": {
                     "kind": "SCALAR",
-                    "name": "ID",
+                    "name": "UserID",
                     "ofType": null
                   },
                   "defaultValue": null