Added line highlighter enhancement

[Jugen]

This PR is for RFE #841 adding the following API to GenericStyledArea:

setLineHighlighterFill( Paint highlight )
setLineHighlighterOn( boolean show )
isLineHighlighterOn()

The highlighter can be styled via CSS using selectors from Path, Shape, and Node. For example:

.styled-text-area .line-highlighter { -fx-fill: lime; }
/* or */
.line-highlighter { -fx-highlight-fill: lime; }

Any added custom Selections can now also be styled via CSS using the selection's name.

[garybentley]

This works great, thanks for adding it. There is just one issue though, if the line is empty, if the paragraph has zero length, then the highlight isn't shown.

[garybentley]

Just one other thing, if the line highlight paint is set it is overriding the default text selection paint.

In my stylesheet I have:

.selection
{
    -fx-fill: blue;
}

And am setting the line highlight paint via code, thus:

area.setLineHighlighterFill(Color.red);

Any selected text on that line has a red background rather than blue thus masking what text is selected.

[Jugen]

Ok, I've made some changes that hopefully resolve the issues you reported.
Can you please test and let me know, thanks.

[garybentley]

Yes that fixed both issues. Thanks.

[garybentley]

Found another issue with this I'm afraid. The highlight can sometimes be "half" applied.

In the screenshot below you can see that the line highlight is only partially rendered. This is on a wrapping line and occurs after I resize (by a splitpane dragger) the left hand component to be larger. The text area contracts but the highlight will often not be fully rendered. Moving the caret to another line renders the highlight properly.

[garybentley]

There is another issue with this. I've added it here to keep things in the same place, hope you don't mind. I don't want to spam up the issues list.

If you have the line highlighter enabled and type at the start of the line then the highlight isn't drawn on the newly added text.

See below.

[Jugen]

Thanks, I've fixed this.