Fix #4016: Translated tags failing to find some tags.

* Normalize spaces to underscores when saving other names. Preserve case
  since case can be significant.

* Fix WikiPage#other_names_include to search case-insensitively (note:
  this prevents using the index).

* Fix sources to return the raw tags in `#tags` and the normalized tags
  in `#normalized_tags`. The normalized tags are the tags that will be
  matched against other names.

app/models/wiki_page.rb

@@ -32,7 +32,9 @@ class WikiPage < ApplicationRecord
     end
 
     def other_names_include(name)
-      where("wiki_pages.other_names @> ARRAY[?]", name.unicode_normalize(:nfkc))
+      name = normalize_other_name(name).downcase
+      subquery = WikiPage.from("unnest(other_names) AS other_name").where("lower(other_name) = ?", name)
+      where(id: subquery)
     end
 
     def other_names_match(name)
@@ -146,7 +148,11 @@ class WikiPage < ApplicationRecord
   end
 
   def normalize_other_names
-    self.other_names = other_names.map { |name| name.unicode_normalize(:nfkc) }.uniq
+    self.other_names = other_names.map { |name| WikiPage.normalize_other_name(name) }.uniq
+  end
+
+  def self.normalize_other_name(name)
+    name.unicode_normalize(:nfkc).gsub(/[[:space:]]+/, " ").strip.tr(" ", "_")
   end
 
   def skip_secondary_validations=(value)