8231602: Deprecate Thread.suspend/resume for removal

[Alan Bateman]

I brought up the issue of deprecating, for removal, 
Thread.suspend/resume a few weeks ago [1]. Mark said "Got for it", no 
other replies or objections.

Here's the webrev with the changes to deprecate-for-removal 
Thread.suspend/resume, ThreadGroup.suspend/resume, and 
ThreadGroup.allowThreadSuspsion:
    http://cr.openjdk.java.net/~alanb/8231602/webrev/index.html

The resulting javadoc is clear that the method is deprecated for removal 
and there is already text and a link to a supporting document so I don't 
think any more is needed.

The CSR is here, I think Stuart plans to look at it.
    https://bugs.openjdk.java.net/browse/JDK-8232655

-Alan

[1] 
https://mail.openjdk.java.net/pipermail/core-libs-dev/2019-September/062571.html