Review request: 8194871: Fix mistakes in FX API docs

[Nir Lisker]

Hi Kevin,

Please review the attached webrev.

I addressed a few fixes I found as I was working, so they are not listed in
the JIRA report.

About Transition#getParentTargetNode:
The current behavior of parent-child relationship is that an animation can
be added to multiple parent transitions. Each parent transition will see
that animation as its child, however, the child will see only one of those
animations as its parent - the one to which is was added last. This
asymmetry is a recipe for trouble (and I argue should be addressed at some
point).
For this reason, the doc does not specify the "last one wins" behavior, so
that no contract is created. This means that it's not clear which parent is
going to be queried on each (recursive) invocation.

Most of the changes could be backported to 8 and 9. In 9, the methods
getRangeShape and getUnderlineShape of TextAreaSkin are also missing
documentation.