Keep services updated of added views.

We were marking subtree events as not important for
accessibility based on the root view, but that doesn't
take into account the fact that important children may have
changed. In particular, adding a View to the hierarchy was
sometimes marked as not important because the layout it was
attached to was not important.

Also fixing an issue with UiAutomation where it called out
to the test filter with a lock held.

Also fixing an issue where nodes that are the source of
accessibility events are always marked as important for
accessibility.

Bug: 31226561
Change-Id: Ib619948ba1bbcfd00aef1d10726152f6cf2dfccd