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

[Nir Lisker]

The usual doc fixes (for OpenJFX 16).

Can wait until RDP2 to see if something else comes up.

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

Commit messages:
 - Initial commit

Changes: https://git.openjdk.java.net/jfx/pull/380/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=380&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8252389
  Stats: 19 lines in 4 files changed: 1 ins; 1 del; 17 mod
  Patch: https://git.openjdk.java.net/jfx/pull/380.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/380/head:pull/380

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