RFR: JMC-6555 Convert JOverflow plugin to SWT

[Arvin Kangcheng Xu]

Hello all,

This change aims to port JOverflow from using JavaFX to SWT/JFace, so
the extra dependencies could be dropped. Additionally, this change
makes JMC-6343 is no longer valid.

This port (re)implements all features available in the original
version, and UI design is kept as close as possible. Please let me
know your thoughts. Thank you very much!

Also, thanks Jie for creating this webrev for me!

Webrev:
https://cr.openjdk.java.net/~jkang/joverflow-swt/webrev.01/
Bug:
https://bugs.openjdk.java.net/browse/JMC-6555

Regards,
Kangcheng