Update VE core submodule to master (52dc4e8)

New changes:
8420735 Test cases for annotating handles own children nodes
a3395ae Improve equalRange assertion and use in more places
52ee587 Block item drag and drop
dfe6d9f Drag and drop of arbitrary selections
11ffd9a Defer focusableNode selection fix until after native selection change

Change-Id: Iffebd8c7e8fbb7c17e25984d69e692b0c0980950