Fix mistakes in FX API docs

Issue for collecting API doc fixes for OpenJFX15:

1. VBox constructor : "spacing - the amount of horizontal space between each child" -- should be vertical

2. VBox#setVgrow : "value - the horizontal grow priority for the child" -- should be vertical
(see JDK-8244820)

3. introduction_to_fxml.html : "attribute that points to a handler method with a ListChangeListner.Change" -- should be "ListChangeListener"

4. Text#fontSmoothingTypeProperty : "The width of the bounding box is defined by the widest row." -- sentence should be removed (looks like a copy/paste error)

5. Cell#commitEdit​(T newValue) : first sentence (summary) description is broken

6. In the pakage javafx.css [1], some classes in and their methods are missing docs (deferred to JDK-8250590)

7. Transition: "In addition an extending class" missing a comma

[1] https://openjfx.io/javadoc/14/javafx.graphics/javafx/css/package-summary.html