[jfx16] RFR: 8252389: Fix mistakes in FX API docs

[Kevin Rushforth]

On Mon, 18 Jan 2021 15:07:34 GMT, Nir Lisker <nlisker at openjdk.org> wrote:

> The usual doc fixes (for OpenJFX 16).
> 
> Can wait until RDP2 to see if something else comes up.

@nlisker I'll wait to review this until after you add the fix noted in [JDK-8260430](https://bugs.openjdk.java.net/browse/JDK-8260430).

-------------

PR: https://git.openjdk.java.net/jfx/pull/380