Send hover to all children under pointer.

Previously we only sent hover to the topmost child, but this doesn't
handle cases where multiple children are overlapped to achieve
certain special effects.  Now we send hover to all children until
one of them handles it.

Also moved the call to send the accessibility event into the
main dispatch function so that we can send the accessibility event
for all innermost hovered views even when setHovered() might
not be called.

Change-Id: I6fb8b974db44b594c441deafc012b8415afdfac7