RFR: Unclutter ShenandoahHeap (multiple changes)

[Roman Kennke]

Looks good. Thanks!
Roman

> http://cr.openjdk.java.net/~shade/shenandoah/unclutter-sh-heap/webrev.01/
> 
> This is a bulk webrev that tries to unclutter the main ShenandoahHeap class, before we try and
> rearrange some of the declarations. I deliberately split it in several changesets to simplify
> backports. A brief tour of changes:
> 
>  *) Homogenize unimplemented stubs handling. This removes most of the stubs that have
> ShouldNotReachThere/ShouldNotCallThis/Unimplemented in favor of our clear-cut define. Those stubs
> are needed to match the overly-wide upstream interface, but nothing actually calls those stubs if GC
> does not want it.
> 
>  *) Remove unused alloc-seq recording for start/end of GC cycle. It was there for partial
> heuristics, and it is not needed now. These methods are slowly bit-rotting and clutter the ShHeap.
> 
>  *) Move ShenandoahAllocType and ShenandoahAllocRequest to separate file. This cuts down the clutter
> in ShHeap by moving the 200+ line definition into the separate file.
> 
>  *) Inline ShHeap::prepare_concurrent_evacuation. The method has only one use, and it is small to be
> inlined into op_final_mark.
> 
>  *) Inline ShHeap::fixup_roots. The method has only one use, and it can be inlined right at use.
> 
>  *) Remove ShHeap::region_in_collection_set in favor of SHR::in_cset. We already have this data in
> region status, there is no need to keep the separate method for it. Verifier still checks the
> collection set view and region statuses are in sync.
> 
>  *) Inline ShHeap::do_marked_object_complete. The method was a convenience for two asserts it had.
> Can be inlined right at use to declutter ShHeap.
> 
>  *) Rename concurrentMark -> concurrent_mark. Obvious camelCase removal.
> 
> Testing: tier3_gc_shenandoah {fastdebug|release}
> 
> Thanks,
> -Aleksey
>