Add `valid_roles` property to group members

Part of a larger initiative to convert the group members page from
HAML to Vue

app/helpers/groups/group_members_helper.rb

@@ -44,7 +44,8 @@ module Groups::GroupMembersHelper
           id: source.id,
           name: source.full_name,
           web_url: Gitlab::UrlBuilder.build(source)
-        }
+        },
+        valid_roles: member.valid_level_roles
       }.merge(member_created_by_data(member.created_by))
 
       if member.invite?

app/serializers/group_group_link_entity.rb

@@ -22,6 +22,10 @@ class GroupGroupLinkEntity < Grape::Entity
     expose :group_access, as: :integer_value
   end
 
+  expose :valid_roles do |group_link|
+    group_link.class.access_options
+  end
+
   expose :shared_with_group do
     expose :avatar_url do |group_link|
       group_link.shared_with_group.avatar_url(only_path: false)

spec/fixtures/api/schemas/entities/group_group_link.json

 {
   "type": "object",
-  "required": ["id", "created_at", "expires_at", "can_update", "can_remove", "access_level"],
+  "required": [
+    "id",
+    "created_at",
+    "expires_at",
+    "can_update",
+    "can_remove",
+    "access_level",
+    "valid_roles"
+  ],
   "properties": {
     "id": { "type": "integer" },
     "created_at": { "type": "date-time" },
@@ -15,6 +23,7 @@
         "string_value": { "type": "string" }
       }
     },
+    "valid_roles": { "type": "object" },
     "shared_with_group": {
       "type": "object",
       "required": ["id", "name", "full_name", "full_path", "avatar_url", "web_url"],

spec/fixtures/api/schemas/group_member.json

@@ -7,6 +7,7 @@
     "access_level",
     "requested_at",
     "source",
+    "valid_roles",
     "can_update",
     "can_remove",
     "can_override"
@@ -36,6 +37,7 @@
         "web_url": { "type": "string" }
       }
     },
+    "valid_roles": { "type": "object" },
     "created_by": {
       "type": "object",
       "required": ["name", "web_url"],