Fix OptionGroup elements losing focus on value change (#10451)

The misbehavior was caused by VOptionGroup.buildOptions recreating
associated panel on every change by removing and adding new elements.
With this fix applied it tries to update existing elements,
distinguishing them by assigned keys. It will recreate panel though if
elements are reordered or new elements were added/removed.

Change-Id: I1245b2ff30ce1932614c1eac37bd0131cbd29dd7