RFR [9] 8140687: Move @Contended to the jdk.internal.vm.annotation package

[Fabian Lange]

Hi,

Without some good argument against it, I think the only issue
> is where (what package) to place it. Carrying it out from there seems
> identical to your webrev diffs, just changing import statements
> and the like.
>

Doug, as you mention java.util.concurrent. I think that should be the place
for a concurrency support annotation. I wouldn't necessarily agree that
this is an esotheric annotation. I could argue that writing efficient
multithreaded programs is more common than any UI or even sound related
functionality in the JDK.
@Contended is important for making the JDK a tool for writing fast code. I
was so happy to see it come, and would be sad to see it go.

Fabian