BURs: change mass updates to not remove left-hand side tags.

Change mass updates to not automatically remove the left-hand side tags
from the post. This won't work with full boolean searches in the future
and already doesn't work with complex searches involving metatags or OR-tags.

app/logical/bulk_update_request_processor.rb

@@ -264,14 +264,11 @@ class BulkUpdateRequestProcessor
   end
 
   def self.mass_update(antecedent, consequent, user: User.system)
-    normalized_antecedent = PostQueryBuilder.new(antecedent).split_query
-    normalized_consequent = PostQueryBuilder.new(consequent).parse_tag_edit
-
     CurrentUser.scoped(user) do
-      Post.anon_tag_match(normalized_antecedent.join(" ")).reorder(nil).parallel_each do |post|
+      Post.anon_tag_match(antecedent).reorder(nil).parallel_each do |post|
         post.with_lock do
-          tags = (post.tag_array - normalized_antecedent + normalized_consequent).join(" ")
-          post.update(tag_string: tags)
+          post.tag_string += " " + consequent
+          post.save
         end
       end
     end

test/unit/bulk_update_request_test.rb

@@ -326,7 +326,7 @@ class BulkUpdateRequestTest < ActiveSupport::TestCase
         end
 
         should "update the tags" do
-          assert_equal("bar baz", @post.reload.tag_string)
+          assert_equal("bar baz foo", @post.reload.tag_string)
           assert_equal("approved", @bur.reload.status)
           assert_equal(User.system, @post.versions.last.updater)
         end
@@ -575,7 +575,7 @@ class BulkUpdateRequestTest < ActiveSupport::TestCase
       end
 
       should "process mass updates" do
-        assert_equal("bar baz bbb blah", @post.reload.tag_string)
+        assert_equal("aaa bar baz bbb blah", @post.reload.tag_string)
       end
 
       should "set the alias/implication approvers" do