Centralize parser attaching inside ContainerNode

Move all parser attach() and lazyAttach() calls into ContainerNode::parserAppendChild
and parserInsertBefore. This means callers no longer need to manually check if they
need to attach the newly inserted child removing a bunch of code. It also means
you can turn on parser lazy attach in both XML and HTML by just changing one function
in ContainerNode.cpp

BUG=276687

Review URL: https://chromiumcodereview.appspot.com/23459004

git-svn-id: svn://svn.chromium.org/blink/trunk@156764 bbb929c8-8fbe-4397-9dbb-9b2b20218538