[11] RFR: Split Shenandoah C2 rules into separate .ad files

[Roman Kennke]

Yes this is good.

Thanks,
Roman


> https://cr.openjdk.java.net/~shade/shenandoah/11u-split-ad/webrev.01/
> 
> This does what our later releases do: split Shenandoah rules into separate .ad files. This
> alleviates quite a bit of upstream exposure and also makes backports from dev easier. After this
> change, there are no differences against upstream in x86_32.ad and x86_64.ad. There are still some
> minor leftovers in aarch64.ad. New files are also very close to the versions in jdk/jdk.
> 
> Testing: {x86_32, x86_64, aarch64} hotspot_gc_shenandoah
>