Fix #3696: API: handle boolean params consistently

* Use ApplicationRecord#attribute_matches to handle boolean attributes
  consistently in search methods.

* Add support for searching various boolean attributes that previously
  weren't supported.

app/models/artist.rb

@@ -566,17 +566,8 @@ class Artist < ApplicationRecord
         q = q.url_matches(params[:url_matches])
       end
 
-      if params[:is_active] == "true"
-        q = q.active
-      elsif params[:is_active] == "false"
-        q = q.deleted
-      end
-
-      if params[:is_banned] == "true"
-        q = q.banned
-      elsif params[:is_banned] == "false"
-        q = q.unbanned
-      end
+      q = q.attribute_matches(:is_active, params[:is_active])
+      q = q.attribute_matches(:is_banned, params[:is_banned])
 
       if params[:creator_name].present?
         q = q.where("artists.creator_id = (select _.id from users _ where lower(_.name) = ?)", params[:creator_name].tr(" ", "_").mb_chars.downcase)