JDK-8208761: Update constant collections to use the new immutable collections

[Nir Lisker]

Hi All,

Iv'e been working on updating OpenJFX to use the Java 9 immutable
collections [1]. If you know of any additional location which can be
updated, please add a comment or reply here.

New code should be mindful of these collections' existence (contributors
and reviewers alike) so that we don't need to continuously iterate over the
platform to update it.

[1] https://bugs.openjdk.java.net/browse/JDK-8208761

Thanks,
Nir