Results 2 issues of JFormDesigner

This PR fixes a painful behavior that I noticed in [Markdown Writer FX](https://github.com/JFormDesigner/markdown-writer-fx): When I start typing into the current line, RichTextFX immediately scrolls the current line to the top...

**Note**: this PR should be **not yet merged into master** because it does not work correctly as long as the JDK bug (see below) is not fixed. Created the PR...