Support Using javafx.web in Custom Components

[remmymilkyway]

It would be great if SceneBuilder could support adding custom components that use classes javafx.web (e.g. javafx.web.WebView).

Expected Behavior

It should accept components that require javafx.web.

Current Behavior

When I try to import such a component, the selection turns out to be blank

Context

A complete description of the issue and what I've tried can be found in this StackOverflow post.