Updated migrateStartMetas to handle migrate both start/end metas

* As a mirror transformation to migrateStartMetas, migrate
  template marker end-metas that are last-children to their
  parent's sibling. This has the same benefit as the former
  transformation of more accurately bounding template-generated
  content.

* One selser test fails -- but arguably, a better result given that
  the parse output is a bit broken on this test case.

Change-Id: I5ca7caf5124acd91be8c6f1d4308f85e3f5daf4f