Update VE core submodule to master (bc37479)

Authored by Jdforrester-WMF.


Update VE core submodule to master (bc37479)

New changes:
eab6467 Add ve.dm.Document#getLength
310a040 ve.ui.Tool: Correct documentation
7a64825 Localisation updates from https://translatewiki.net.
d025658 ve.utils: Add ve.binarySearch() and port ve.dm.MetaList#findItem to it
8400efd demo: Fix another bug showing both LTR and RTL stylesheets
d3168f3 Factor out method which fills paste target with dummy contents for copy
363c804 Remove platform auto-instantiation
67ac409 Improve demo read mode
c2588bd Replace abstract functions that just throw with null
9073b6b Add docs for ve.ui.ContextItem#embeddable

Change-Id: I41b0ec10e0c085290944e8c3293bcad5e956e909